NOAA Technical Memorandum NMFS NE 113
Individual
Vessel Behavior in the Northeast Otter Trawl
Fleet during 1982-92
by Barbara
Pollard Rountree
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
Print
publication date October 1997;
web version posted August 16, 2001
Citation: Rountree BP. 1997. Individual
Vessel Behavior in the Northeast Otter Trawl
Fleet during 1982-92. US Dep Commer, NOAA Tech Memo NMFS NE 113; 50 p
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Abstract
This
paper characterizes otter trawl fleet activity in the northeastern United
States from an individual vessel perspective. An individual vessel
time series data base was created from the National Marine Fisheries
Service’s commercial fisheries landings weighout data base covering 1982-92. The
distributions of such annual variables as number of trips, number
of ports at which landed, number of species landed, number of statistical
areas in which fished, number of days absent, weight landed, and revenue
are presented across three vessel size classes. The central tendencies
and variability in these individual vessel attributes are presented.
Observations on individual vessel behavior, as well as a discussion of
the applicability of the individual vessel data base approach, are also
presented.
INTRODUCTION
There
is not a consistent, widely held, complete picture of how any of the
fishing fleets in the northeastern United States operate. The perceptions
of such fleet operations, as gleaned from the standard aggregate statistics
about the region’s fisheries are, at best, partial. Further, the
perceptions do not reveal much about the decision-making behavior (“behavior”)
of individual fishing vessels within any of the fleets.
The change in fisheries management in the Northeast to direct control
of individual vessels in some fisheries (i.e., allotment to individual
vessels of an annual number of days at sea), and the trend toward controlled
access to specific fisheries, will make an understanding of individual
vessel behavior critical to the success of fisheries management. Analysis
of such behavior will permit optimum design, monitoring, and control
of these fisheries management measures, and would apply particularly
well in a multispecies fisheries environment.
Information about individual vessel behavior resides in the National
Marine Fisheries Service’s (NMFS) Northeast Fisheries Science Center’s
(NEFSC’s) commercial fisheries data bases, but has not been tapped because
the procedures needed to extract it are cumbersome, and because until
recently, the interest in individual vessel behavior and fleet operations
was secondary.
Recently, however, a working group consisting of members from the NEFSC’s
Population Dynamics Branch and Social Sciences Branch has been established
to facilitate complementary and multidisciplinary research on Northeast
fleet operations, based on individual fishing vessel behavior. A
major objective of the working group is to encourage modeling of temporal
and spatial effects in such operations and behavior. For example,
although most major fisheries are pursued by some vessels dedicated strictly
to that fishery, switching into and out of that fishery by other vessels
often occurs in response to seasonal opportunities, market conditions,
stock statuses, and more. This switching can create significant,
interannual, unbalanced movement among fisheries.
This paper presents the results of an initial characterization of the
Northeast otter trawl fleet. This characterization is based on
a single individual vessel time series (IVTS) data base which was created
from the NEFSC’s commercial fisheries weighout data base. This
IVTS data base consists of 36 variables, and covers the 1982-92 period. The
unit of organization and analysis (i.e., file definition) within
the IVTS data base is an individual vessel’s activity through a calendar
year. Each file summarizes activity according to such variables as number
of trips, trip length, number of ports at which landed, number of statistical
areas in which fished, number of calendar months in which fished, and
number of species landed.
This characterization serves several purposes: 1) indicating what
time series information exists in the weighout data base; 2) examining
the robustness of the existing data and the data collection system to
support individual vessel analyses; 3) exploring the difficulty of creating
time series data bases from the existing data structure; and 4) assessing
the value of obtaining software to make IVTS files available to analysts.
The following section of this paper, “Methods,” includes
a brief background on the region’s data collection system as a basis
for understanding the study’s methods. The section then describes
data collection, storage, and preparation practices, variable definitions,
and methods used in screening the data and generating the IVTS data base.
The “Results” section includes a brief
background on the region’s fisheries as a framework for understanding
the results. The section then refers to tables describing the variable
values, summed on an annual basis for individual vessels, and broken
out by tonnage class.
The “Discussion” section focuses on issues
of data coverage and sampling, variable selection and accuracy, and the
general IVTS data base approach. Because this paper is more of
an evaluation of the general usefulness of weighout data and of the IVTS
data base for providing individual vessel behavior information, than
an evaluation of the specific findings on such behavior in the Northeast
during 1982-92, the discussion has more analyses of data and data base
issues than of individual vessel behavior findings. The examination
of the data raises several questions about data definition, measurement,
collection, sampling, and quality control. Because the data have
not previously been exposed to this type of analysis, the majority of
these questions have not been answered.
A set of “Conclusions and Recommendations” complete
the report.
METHODS
BACKGROUND
The NMFS is attempting to enhance its systems for collecting, archiving,
and analyzing fisheries catch and effort data to support the increasingly
complex needs of fisheries management. As part of the effort to
enhance the data collection system, mandatory reporting by dealers and
vessels was implemented in 1994. Until the mandatory reporting
system was implemented, a voluntary system existed which relied on port
agents collecting catch and effort data for vessels of at least 5 gross
registered tons (GRT) landing in the NMFS Northeast Region (i.e.,
from Cape Hatteras to the Canadian border). These voluntarily supplied
data, covering the 1982-92 period, have been the basis for this paper.
DATA COLLECTION AND
STORAGE
The voluntary data collection system consists of three tiers. The
first tier is landings data which are compiled from dealer weighout slips
(i.e., receipt records) which provide the landed weight of the
catch by species, vessel, and trip. The second tier is effort data
which are collected through interviews with the vessel operators conducted
in port at the time of landing. These interview records contain
the most reliable trip information on variables such as gear type, fishing
location, depth, and effort. The third tier is tow-by-tow data
which were collected in the early years of the 1982-92 period at sea
by port agents sailing on commercial fishing vessels, and collected in
the later years of the period by contract personnel sailing on the vessels
(i.e., the sea sampling program).
Since all three tiers depend
on voluntary cooperation, the percentage of total landings in the Northeast
which has been recorded by the weighout
slip process is not known. Twenty-eight percent of trips for which
weighout slips existed in 1992 resulted in interviews by port agents. For
multiple-day trips, the interview rate was approximately 50%; for day-boat
trips, the rate was approximately 15%. For the remaining trips
(i.e., noninterviewed), port agents estimated fishing effort,
gear, and location based on their knowledge of the particular vessel’s
activity and the activities of similar vessels operating in the same
general area.
The voluntary system of data collection came into being in 1964, originating
with Maine, Massachusetts, and Rhode Island. The system added New
Jersey in 1978, Maryland and Virginia in 1981, New Hampshire in 1982,
New York in 1986, and Connecticut and Delaware in 1989. Problems
exist with the data collected in New York in that, because of fish handling
practices there, an individual vessel is not able to be identified in
the data base when no interview occurred.
The data base structure for storing these voluntary data has also evolved
since 1964. Because of technical aspects of the data collection
and storage process, difficulties and uncertainties exist for data collected
prior to 1982. The difficulties and uncertainties occur when one
associates the weighout landings data from an individual trip with the
corresponding interview data. For this reason and because of changes
in the structure of the computer data bases themselves, the analyses
in this paper are limited to data collected from 1982 to 1992.
DATA PREPARATION,
ANALYSIS, AND PORTRAYAL
This study includes those vessels which used otter trawl gear exclusively
throughout the year. Vessels that used other gear or a combination
of otter trawls and other gear were not examined.
Otter trawl vessels were divided into three categories based on their
GRT, following the traditional classes used by the NEFSC for this fleet. Tonnage
class (TC) 2 contains vessels that are 5 to 50 GRT, TC3 contains vessels
that are 51 to 150 GRT, and TC4 contains vessels that are 151 or more
GRT.
A single data file which contains the available cumulative annual landings
weight, landings revenue, and effort statistics for each vessel was created
as the basis for the analyses. Weight landed values are given as
the live weight equivalents in metric tons for all species combined for
a given vessel. Revenue values are given as total nominal dollars
(i.e., not adjusted for inflation) for all species landed by a
given vessel. Each vessel was identified by its six-digit identification
(i.e., permit) number which is assigned as part of the federal
fishing permitting process.
Landings per unit of effort (LPUE) statistics were calculated as the
simple ratio of the annual cumulative landings (both as weight and revenue)
of a vessel divided by the annual cumulative nominal effort of that vessel. Two
measures of effort were examined: 1) number of trips, and 2) number
of days absent. The days absent measure was recorded to the nearest day,
and includes the time between when a vessel left and returned to port.
For some individual trips, effort statistics were either missing or
inconsistent (e.g., the amount of time trawling exceeded the length
of the trip). While the number of trips in which these problems
occurred were relatively small, not accounting for these problems in
the data resulted in large distortions in some of the preliminary analyses
(particularly those involving landings rates by individual vessels). To
utilize information from as many vessels as possible, procedures were
developed for screening and, where possible, for adjusting the effort
data for missing or inconsistent values. Such adjustments to effort
data were based on the performance by that vessel during the rest of
the year in question. When such adjustments were not possible for
a given vessel, then that vessel was eliminated from those statistical
results which required effort data. Consequently, the total number
of vessels will vary slightly among some of this study’s statistical
results.
The resulting statistical information about fleet behavior has been
presented as tables displaying an annual time series of frequency distributions
of the various fishery statistics. In the tables, one axis contains
the years 1982 through 1992, while the other axis contains intervals
of values of the variable of interest. To provide better resolution
across the spectrum of values for some individual vessel behavior variables
and for some vessel size classes, it was necessary to define intervals
of unequal size, with higher resolution at the lower end of the spectrum.
Within the cells of the tables are numbers which are, in most instances,
counts of vessels which fall into that year and variable interval. A
vessel is included in a particular cell because of the measure of its
activity over the course of the year. In most cases, this measure
is a summing of events, such as number of trips in a year or number of
statistical areas in which fished in a year. In a few cases, though,
this measure is an average such as the annual average trip length for
that vessel.
RESULTS
BACKGROUND
The total number of vessels in all Northeast fisheries grew considerably
after passage of the Fishery Conservation and Management Act in 1976
(Conservation and Utilization Division 1993). According to the
weighout data base, the total number of vessels in the region of 5 GRT
or more grew from 1,245 in 1978 to 1,891 in 1992. Most of this
growth occurred by 1984, and among those vessels using otter trawls.
The overall ex-vessel (i.e., dockside) revenue of landings by
all Northeast vessels grew steadily from 1978 to 1984, and from then
until 1992 varied around a mean of about $470 million dollars in nominal
terms. The weight of landings followed the same trend, and was
around 707,000 metric tons (mt). These values do not reflect increases
in the cost of fishing nor in the amount of time spent fishing, both
of which have increased over the 1978-92 period.
In the NMFS Northeast Region in 1982, 1,193 otter trawl vessels each
landed an average of almost 2.4 mt per day at sea. In 1992, with
1,012 vessels fishing, this value dropped to below 1.7 mt per day. Revenue
per day at sea rose in nominal terms between 1982 and 1992, but in real
terms (i.e., adjusted for inflation) fell over the 11-yr period
from $2,110 to $1,600.
Given this history of aggregate fleet behavior, I examined the annual
frequency distribution of 13 variables of individual vessel behavior
over 11 yr for three vessel size classes.
VARIABLES
Number of Vessels
All Gear Types
In 1992, 39% of TC2 vessels used otter trawls exclusively (Table
1). Other important gear for TC2 vessels in 1992 included “other
gear” (34%) and gill nets (15%). (“Other gear” includes all gear
except otter trawls, gill nets, scallop dredges, and/or clam dredges.) The
reliance on otter trawls exclusively declined from the mid 1980s, from
a peak of 56% in 1986 to 39% in 1992.
The majority (58%) of TC3 vessels used otter trawls exclusively in 1992 (Table
2). Other important gear or combinations of gear for TC3
vessels in 1992 included “other gear” (18%) and scallop dredges only
(10%). The heavy reliance on otter trawls was consistent over
the years of the study. The exclusive use of scallop dredges
increased over the period, while the exclusive use of clam dredges
peaked in 1986.
Beginning in 1989, more TC4 vessels relied on scallop dredges alone
than on otter trawls alone (Table
3). The percentage of TC4 vessels fishing exclusively with otter
trawls during the study period remained relatively steady (i.e.,
ranging between 32 and 38%), while the percentage of those fishing exclusively
with scallop dredges nearly doubled (i.e., from 25 to 47%). Together,
those vessels using scallop dredges alone (47%) or otter trawls alone
(33%) comprised 80% of the TC4 fleet in 1992.
Otter Trawls
From 1982 to 1992, the number of TC2 otter trawl vessels declined
by about 100, while the number of TC3 vessels grew and then declined
to its original number (Table
4). The TC4 vessels, comprising only about 10% of the fleet,
experienced this same upward and downward shift as the TC3 vessels over
the time period.
Year Built
As of 1992, the TC2 otter trawl fleet had the oldest composition, with
5% being built prior to 1941, 22% prior to 1951, and 54% prior to 1976,
leaving 46% being built since 1976 (Table
5).
As of 1992, only 13% of the TC3 otter trawl fleet was built prior to
1966, while 74% was built between 1966 and 1980 (Table
6).
The trend toward younger vessels is strongest among the TC4 otter trawl
fleet. As of 1992, the TC4 otter trawl fleet contained very few vessels
(10%) built prior to 1976, with the heaviest construction period being
1976-80 (Table 7).
Number of Trips
In this variable, a phenomenon is encountered in which a significant
percentage of both large and small vessels appear to take very few trips
per year. For the 1982-92 period, a significant percentage of TC2
vessels made less than 11 trips per year, but in addition, a significant
percentage of vessels made more than 100 trips per year (Table
8). This distribution is consistent across all 11 yr. The
TC2 vessels were most likely of any class of vessel to have made more
than 100 trips in any given year. They were also just as likely
as the larger vessels to have made less than 11 trips per year.
Throughout the 11-yr period, the majority of TC3 vessels fished 30 or
fewer trips per year (Table
9). By 1992, 31% of TC3 vessels made between 21 and 30 trips
per year. For the 1982-92 period, the distribution of the number
of trips per TC3 vessel was skewed toward the low end of the defined
intervals.
The TC4 vessels predominately fished between 21 and
30 trips per year (Table
10). Only a handful of such vessels fished more than 40 trips
in a given year.
Trip Length
The smaller TC2 vessels had average trips of shorter duration than larger
TC3 and TC4 vessels during 1982-92. No TC2 vessels made trips longer
than 11 days. In 1992, 95% of TC2 vessels had an average
trip length of less than or equal to 3 days (Table
11).
Over the study period, between 32 and 41% of TC3 vessels had average
trips of less than or equal to 3 days (Table
12). An additional 15-30% had an average trip of 4-5 days,
20-25% had an average trip of 6-7 days, and 11-24% had an average trip
of 8-9 days. Over the study period, this mid-size otter trawler class
tended toward longer trips.
During 1982-92, TC4 vessels generally fished for a greater period of
time on each trip when compared to the smaller size classes (Table
13). By 1992, almost half of all TC4 vessels had trips which
averaged 8-9 days; few such vessels had average trips of more than 9
days.
Number of Ports
at Which Landed
The number of ports visited annually by a single vessel was usually
one or two, with occasional values up to six for TC2 and TC4 vessels,
and up to seven for TC3 vessels (Table
14, Table 15, Table 16).
The percentage of TC2 vessels landing at one port increased from 65%
in 1982 to 80% in 1988, then declined to 72% in 1992. The percentage
of these vessels landing at two ports declined from 27% in 1982 to 13%
in 1988, then increased to 20% in 1992. About 90% of TC2
vessels landed consistently in either one or two ports over the 11-yr
time frame.
For TC3 vessels, 55% landed at one port in 1982. This value rose
to 71% in 1988, then declined to 54% in 1992. The percentage of
these vessels landing at two ports declined from 32 to 22% between 1982
and 1988, then increased to 34% in 1992.
The percentage of TC4 vessels landing at one port rose from 49% in 1982
to 75% in 1987, then declined to 58% in 1992. The percentage of
these vessels landing at two ports declined from 34 to 18% between 1982
and 1987, then increased to 28% in 1992.
Number of Statistical
Areas in Which Fished
The TC2 vessels fished in a maximum (in 1985) of nine different statistical
areas (SAs) during 1982-92; however, an annual average of 94% of these
vessels fished in a maximum of only three SAs over the 11 yr (Table
17). Less than 1% of the TC2 vessels on average fished in more
than five SAs.
Over the study period, an annual average of only 2% of TC3 vessels fished
in more than eight SAs, while an annual average of 88% fished in 1-6
SAs (Table 18). In
1982, those TC3 vessels fishing in 1-6 SAs were distributed fairly uniformly
among the six categories. By 1992, only 8% fished in just one area,
while 67% fished in four or more SAs.
During 1982-92, TC4 vessels fished in as many as 10
or more SAs in a year, but on average 82% of the vessels fished in 3-8
SAs, and 54% fished
in 4-6 SAs (Table 19). The
highest annual percentage fishing in just one SA (13%) occurred in 1988,
compared to 3% in 1992.
Number of Calendar
Months in Which Fished
There was a significant percentage of TC2 vessels fishing either only
in 1 mo (e.g., 21% in 1992) or in all 12 mo (e.g., 20%
in 1992) (Table 20). Vessels
which weren’t in these two extreme categories seemed to be evenly distributed
among the other 10 categories. This bimodal distribution held throughout
the 11-yr period.
Most TC3 vessels fished in more months than TC2 vessels. Those TC3 vessels
fishing in all 12 mo predominated, more so in 1992 than in prior years (Table
21). There was a significant percentage of TC3 vessels (between
5 and 12%) fishing in only 1 mo of the year.
The percentage of TC4 vessels fishing in all 12 mo
increased from 31% in 1982 to 66% in 1992 (Table
22). A small proportion (3-10%) of vessels fished in only 1
mo during the 11-yr period.
Number of Species
Landed
The percentage of TC2 vessels landing no more than two species per year
increased significantly over the study period, from 5 to 19% (Table
23). The percentage of TC2 vessels landing between 15 and 17
species per year, the interval that had dominated the 1980s, climbed
from 20% in 1982 to 22% in 1984, then fell to 9% by 1992. There
is a clear trend during the study period toward fewer species being landed
per TC2 vessel per year.
In 1992, most (76%) TC3 vessels landed at least 12 species, with 43%
landing between 12 and 17 species (Table
24). In the 1980s, TC3 vessels were landing fewer species on
average than TC2 vessels. By 1992 that was no longer the case,
as TC3 vessels landed more species on average.
The TC4 vessels had a tighter distribution of the
number of species landed than the smaller vessel size categories (Table
25). Throughout the study period, a majority of these vessels
landed between 9 and 17 species, with a slight trend to land more species
over time.
Number of Days Absent
From 1982 to 1992, between 60 and 70% of TC2 vessels were absent from
port for less than 76 days per year, and between 20 and 30% were absent
for less than 11 days per year (Table
26). The distribution for TC2 vessels is skewed to the left
with most observations clustered within the lower 20% of the overall
range.
From 1982 to 1992, between 50 and 60% of TC3 vessels were absent from
port from 76 to 200 days per year (Table
27). In 1992, 67% of these vessels were absent from port from
101 to 250 days per year, 43% were absent from 151 to 250 days, while
only 6% were absent for less than 11 days.
For TC4 vessels, 50% or more were absent from port
over 150 days per year during the 11-yr period (Table
28). In 1992, over 50% were absent for more than 200 days,
a significant increase in effort from 1991 levels. Between 4 and
16% of these vessels were absent for less than 26 days per year during
the study period.
Weight Landed
For the study period, the distribution of total annual landings is highly
skewed left for all tonnage classes, with most observations clustered
within the lower 10% of the range (Table
29, Table 30, Table 31). Total
annual landings per vessel declined over the study period for all tonnage
classes.
During the study period, total annual landings of most TC2 vessels ranged
from 0 to 200 mt, with a maximum of 1,000 mt. The percentage of
TC2 vessels landing 100 or fewer metric tons per year increased from
75% in 1982 to 88% in 1992.
From 1982 to 1992, total annual landings of most TC3 vessels ranged
from 0 to 500 mt, with a maximum of 5,000 mt. In this tonnage class,
54% of vessels landed 200 or fewer metric tons in 1982, compared to 72%
in 1992.
During the study period, total annual landings of most TC4 vessels ranged
from 0 to 1,000 mt, with a maximum of 5,000 mt. The percentage
of TC4 vessels landing 500 or fewer metric tons per year increased from
44% in 1982 to 69% in 1992.
Weight Landed per
Day Absent
Average weight landed per day absent in all tonnage classes declined
over the study period (Table
32, Table 33, Table 34). The
percentage of TC2 vessels accounting on average for 0.5 or fewer metric
tons per day absent increased from 28% in 1982 to 60% in 1992. Over
the 11-yr period, average weight landed per day absent for most TC2 vessels
ranged from 0 to 1.0 mt, with a maximum of 10.0 mt. From 1982 to
1986, between 20 and 44% of TC2 vessels had average weight landed per
day absent values over 1.0 mt. In 1992, only 10% of these vessels fell
in that range.
Thirty-one percent of TC3 vessels landed on average 1.5 or fewer metric
tons per day absent in 1982 compared to 83% in 1992. During the
study period, landed weight per day absent for most of these vessels
ranged from greater than 0.5 to 2.0 mt, but during the latter part of
the period, the dominant range was from 0 to 1.5 mt. The maximum
average landed weight per day absent for TC3 vessels exceeded 10.0 mt.
The percentage of TC4 vessels landing an average of 2.5 or fewer metric
tons per day absent increased from 24% in 1982 to 69% in 1992. Average
landed weight per day absent for most TC4 vessels ranged over the 11
yr from greater than 1.0 to 5.0 mt, the upper end of the range being
common in 1982, and the lower end of that range being dominant in 1992. The
maximum average landed weight per day absent exceeded 30.0 mt for TC4
vessels.
Revenue
Over the 11-yr period, 62% (range of 56-67%) of TC2 vessels grossed
$50,000 or less per year (Table
35). Twenty-one percent of these vessels (range of 16-24%)
grossed more than $50,000 to $100,000; 14% (range of 12-17%) grossed
more than $100,000 to $200,000. During some years of the study
period, some TC2 vessels grossed up to $500,000, though on average during
the study period, only 3% grossed more than $200,000.
During 1982-92, an average of 25% of TC3 vessels grossed $50,000 or
less per year, while 12% grossed more than $50,000 to $100,000, and 50%
grossed more than $100,000 to $400,000 (Table
36). On average, only 7% grossed more than $400,000 to
$500,000, and only 6% grossed over $500,000.
Over the 11-yr period, the majority of TC4 vessels earned more than
$200,000 to $1,000,000 per year (Table
37). An average of 60% earned more than $400,000 per year,
and between 1 and 10% earned more than $1,000,000 per year. In
1992, 9% earned more than $1,000,000, and only 8% earned $100,000 or
less. Over the period, the overall pattern of revenue distributions
(in nominal terms) shifted slightly to the right.
Revenue per Day
Absent
During the study period, the majority (73%) of TC2 vessels had average
annual revenues per day absent of $1,000 or less (Table
38). In 1992, 92% of these vessels had average revenues per
day absent of $1,500 or less.
Dominant intervals of average annual revenue-per-day-absent values among
TC3 otter trawlers during 1982-92 were: 1) more than $500 to $1,000
(15% on average); 2) more than $1,000 to $1,500 (28%); 3) more than $1,500
to $2,000 (27%); and 4) more than $2,000 to $2,500 (15%) (Table
39). During 1982-92, only 2% of these otter trawlers earned
an annual average of $500 or less per day absent, only 17% earned less
than $1,000, and only 13% earned $2,500 or more per day absent. In
1992, only 19% earned $2,000 or more per day absent.
During 1982-92, 80% of TC4 vessels had average annual revenues per day
absent of more than $2,000, with 6% having average annual revenues per
day absent of more than $5,000 (Table
40). In 1992, only 14% of TC4 vessels had average annual revenues
per day absent of more than $4,000.
DISCUSSION
INDIVIDUAL
VESSEL BEHAVIOR OBSERVATIONS
General Observations
In looking at all 13 statistical variables for all three vessel size
classes of Northeast otter trawlers during 1982-92, one notes that a
number of statistical trends (e.g., trip lengths, number of species
landed, and revenues) often seemed to reverse, and that the turning points
of those reversals often occurred in 1987 or 1988. Many factors
such as changes in fish abundances, seafood demand, and fishery regulations
could have influenced those trend reversals. During the 11-yr study
period, there was little relative variation and only a slight net decrease
in the annual collective abundances of the principal groundfish and flounders
(i.e., 12 demersal species) most sought by the Northeast’s fishermen
(Conservation and Utilization Division 1993). There was a significant
increase up to 1987, then a relative leveling off through 1992, of consumer
demand nationally for seafood species (Fisheries Statistics Division
1993). Perhaps most importantly, though, there were increasingly
more restrictive fishery regulations adopted for Northeast fishermen
in late 1986 (Halliday and Pinhorn 1997); those regulations would have
begun to manifest themselves in their first or second full year of adoption
(i.e., 1987 or 1988).
After implementation of the Fishery Conservation and Management Act
in March 1977, the New England Fishery Management Council (NEFMC) assumed
the lead responsibility for preparing the fishery management plans for
those species most commonly sought by the Northeast’s otter trawlers. The
first such plan -- the 1977 “Fishery Management Plan for Atlantic Groundfish” --
relied on minimum fish sizes, spawning area closures, and maximum harvest
levels for just Atlantic cod, haddock, and yellowtail flounder.
In March 1982, the NEFMC adopted a new, laissez-faire approach to management
of these three species by implementing the “Interim Fishery Management
Plan for Atlantic Groundfish.” The interim plan placed no controls
on fish harvest levels, fishing effort, or fishery participation, but
relied only on minimum fish sizes, minimum mesh sizes, and spawning area
closures, again for just the three species. The interim plan failed
to improve the generally low abundances of two highly sought species
-- haddock and yellowtail flounder.
Consequently, in September 1986, the NEFMC adopted an increasingly restrictive
approach to management of the three species through implementation of
the “Fishery Management Plan for the Northeast Multispecies Fishery.” The
NEFMC used the same fishery management tools as the previous, interim
fishery management plan, but increasingly covered more species, raised
minimum fish sizes, and lengthened spawning area closures, four times
between 1987 and 1993.
That a number of the statistical variable - vessel size class combinations
showed trend reversals soon after the adoption of increasingly restrictive
fishery management regulations would seem to support the goal of using
individual vessel behavior attributes to model otter trawl fleet operations. Such
modeling might ultimately be able to predict the individual-vessel-level
effects of various fishery management regulations, and, in turn, to predict
the likelihood of success or failure of such regulations.
Specific Observations
Results have been presented for 13 variables. Some specific observations
can be made to add to the understanding of the trends during 1982-92
for several of these variables: number of trips, number of days
absent, number of ports at which landed, number of statistical areas
in which fished, number of calendar months in which fished, and number
of species landed.
The results showed a trend for larger vessels to make fewer trips and
smaller vessels to make more trips. This difference is not surprising
given the distinction between “day boats” and “trip boats.” This
variable, numbers of trips, was one in which difficult-to-explain phenomena
appeared, such as when both large and small vessels made very few trips
per year. Independent information would be required to determine
the cause or mix of causes for such low levels of participation. Regional
emigration, mechanical problems, and financial problems are all possibilities.
In addition to the number of trips variable, the days absent variable
was used to measure effort. The days absent variable provides a
general indication of gross fishing time. Variations in steaming
time and time lost due to weather or mechanical difficulties, however,
should be taken into account when comparing this variable to nominal
fishing effort.
The number of ports at which landed variable provides an indication
of the degree to which vessels landed their catch at a port other than
their primary port. A larger number of ports visited in a given
year may indicate an attempt to obtain higher prices at alternate ports,
or fishing activity conducted over a wider geographic range. Many factors
are likely to be involved.
The number of statistical areas in which fished variable is a relatively “soft” statistic,
depending, even for interviewed trips, on fishermen’s recall and/or their
desire to reveal fishing grounds after tiring trips. The number
of statistical areas fished by individual vessels over the course of
a year is related to a variety of factors. Across the fleet, for
example, it may be related to the size of the vessel where a larger vessel
is able to cover a greater distance, or to the species being sought and
the gear being deployed. Changes over the study period in the relative
number of statistical areas being fished may also indicate changes during
that period in the relative distribution/availability of the species
being sought. An increase in the number of statistical areas being
fished by vessels of a given size, for instance, may be caused by an
increase in the amount of searching required for those vessels to make
their catches. Also, in groupings of vessels which use a variety
of gear, we might expect to see a larger number of statistical areas
being fished.
The number of calendar months in a given year in which a particular
vessel was recorded as having fished varies considerably. While
some of this variability may be due to incomplete coverage in certain
years, it may also be explained by vessels which have entered the fleet
since 1982. Unless a new vessel is available to fish in the first
month of its initial year, it will be perceived as having participated
for fewer than the expected number of months. This perception will
be particularly warped for larger vessels which are expected to fish
year-round. A substantial proportion of the perceived outliers
may be due to this initial-entry phenomenon.
As noted, in the 1980s, TC3 vessels were landing fewer species on average
than TC2, possibly because they could travel farther offshore and remain
targeted on fewer but more specific stocks than TC2 vessels. By
1992, this trend reversed, and many other factors influenced what was
brought home for sale. The decline in the predominance of all stocks
of Atlantic cod, haddock, and yellowtail flounder has led to markets
opening up to many more species, for example.
DATA, VARIABLE,
AND DATA BASE ISSUES
Before any attempt can be made to model fleet operations, a number of
data, variable, and data base issues must be addressed and resolved. Those
issues fall into three categories: data coverage and sampling, variable
selection and accuracy, and data base coverage.
Data Coverage
and Sampling
Much of what can or cannot be said about the behavior of individual
vessels depends on the completeness and integrity of the underlying data. During
the period of this study, the implied behavior of some vessels as derived
from the collected data suggests that there may be concerns with data
completeness and integrity. For example, were there TC4 vessels
earning less than $100,000 per year? Were there TC3 vessels fishing
less than 10 days per year? Were there TC4 vessels landing less
than 100 mt per year? There are legitimate reasons why the answers
to these questions could be yes. However, it is difficult if not
impossible in many instances to tell from the existing data whether or
not true vessel behavior was being observed or reported. This section
addresses these concerns from the standpoint of incomplete coverage and
sampling bias.
Incomplete Coverage
Incomplete coverage by the voluntary data collection system could have
occurred for several reasons. Data could have been missed when
vessels landed in remote ports which port agents visited infrequently. Even
if the vessels’ landings data were recorded by cooperative dealers, the
corresponding effort data would have been missed if a port agent did
not conduct interviews with the vessel captains.
Uncooperative dealers, whether in a port agent’s resident port or in
a remote port, could have refused to supply landings data on vessels
from which they bought fish. When this occurred, both landings
and effort data would have been missed by the data collection system.
Data could have been missed when vessels sold either directly to restaurants
or from “roadside” stands. Again, landings and effort data would
have been missed. This direct selling is not as common among TC3
and TC4 vessels as it is among TC2 vessels that land lobster or shrimp
in small Maine ports.
Individual vessel data could have been missed when landings from several
vessels were lumped together on one dealer weighout slip (i.e.,
across-vessel lumping). Unless a vessel happened to be interviewed
soon after landing, there was no way to determine its landings or effort
for that trip based on the lumped-across-vessel dealer weighout slip.
In addition to dealer-based, across-vessel lumping, there was also state-based
lumping in a couple of instances. Connecticut and Delaware have
no port agents, and report only their total landings (i.e., weight
and revenue). There is no way to associate those state-total landings
data with an individual vessel’s landings or effort.
Sampling Bias
Reasons for sampling bias in the voluntary data collection system can
stem from the incomplete coverage noted above, as well as from other
factors. The inability to associate landings and effort data with
a particular vessel due to the problems of incomplete data coverage can
prevent an accurate count of the number of vessels fishing at any point
in time, and bias downward any per-vessel annual statistical averages.
Factors other than incomplete coverage which contribute to sampling
bias include vessel transiency, vessel name/number confusion, otter-trawl-only-use
vessel inclusion, within-vessel lumping, interview nonrandomness, and
data estimation/proration.
When transient vessels from outside the NMFS Northeast Region landed
one or more trips in the region, they were often not identified as transients
on the weighout slips. Consequently, these transient vessels tended
to bias downward the annual per-vessel statistical averages.
When a vessel would change names, the change would sometimes not be
detected by the port agents collecting the data, nor by those auditing
the data, on that vessel. As a result, that vessel’s data would
not be assigned to the correct vessel file -- which is based on the vessel’s
federal fishing permit number -- and two vessel files would be created
inadvertently for one vessel. This vessel name/number confusion
would bias downward the annual per-vessel statistical averages.
Since this study included only vessels that used otter trawls exclusively
throughout the year, and excluded all vessels that used a combination
of otter trawls and other gear, there is opportunity for bias in the
results. The nature and extent of any such bias are unclear, though.
Two analogous, “time saving” practices which could compromise data are:
1) dealers lumping trips from the same vessel onto one weighout slip,
and 2) port agents lumping several weighout slips from the same vessel
fishing in the same area into one computer record (i.e., within-vessel
lumping). The practices of within-vessel lumping are adequate for
generating fleet totals and averages. However, for modeling efforts
which relate landings to effort on a trip-by-trip basis for a given vessel,
these practices have been counter productive. Eliminating from
analysis those data records where these practices occur may cause an
unacceptable loss of data, and, at the same time, bias the remaining
data, although the nature and extent of such bias are unclear.
Most questions about the sampling bias concern the randomness of interview
coverage. A frequency distribution of vessel interviews tends to
be bimodal, with modes near 0 and 100%. It would be expected that
vessels which landed in remote ports and were never seen by port agents
would have never been interviewed. On the other hand, a large number
of vessels were interviewed 100% of the time, meaning that vessels were
not interviewed in a random manner. Nonrandomness may introduce
considerable bias when attempting to model vessel behavior. Again,
the nature and extent of such bias are unclear.
Two types of “data generating” practices which could compromise data
are: 1) port agents estimating and assigning effort and location data
-- based on their judgment of the fishing practices of similar vessels
under similar circumstances (e.g., target species, time of year)
-- to a vessel file for the noninterviewed trips by that vessel; and
2) this study’s proration of missing or inaccurate vessel data -- based
on that vessel’s behavior during the remainder of the calendar year --
for that vessel’s record. There is opportunity for bias as a result
of these practices, but the nature and extent of such bias are unclear.
As noted for several of the bias-creating factors mentioned above, the
nature and extent of such bias are unclear. For some factors, there
is no apparent way to measure the bias after the fact (e.g., vessel
transiency). For other factors, a separate analysis of other existing
data would have to be undertaken (e.g., inclusion of vessels using
a combination of otter trawls and other gear).
Variable Selection
and Accuracy
Whether a vessel’s trip record is based on an interview or not plays
a large role not only in any bias of the data, but also in the accuracy
of any subsequent statistics derived from the data. The following
discussion focuses on the differential effects of interviewed and noninterviewed
data on those statistics which rely on effort and location data. Two
such statistics -- the number of days absent and the number of statistical
areas in which fished -- are covered in more detail.
Interview vs. Noninterview
Effects
Since records from both interviewed and noninterviewed trips were included
in the statistical analyses of vessel activity, not all statistical variables
which were selected from these records can be interpreted with the same
degree of certainty. The accuracy of the variables describing effort
and location (i.e., trip length, days absent, and statistical
areas in which fished), and of those variables which were subsequently
computed (i.e., landings per day absent and revenue per day absent),
depends to a large extent on the proportion of trips which were interviewed.
Instead of having effort and location data for noninterviewed trips
be assigned to trip records based on the judgment and experience of port
agents, an alternative procedure -- proration -- could be devised to
estimate noninterviewed effort and location data, using the interview
data alone as a sample base. A proration procedure would need to
assume that the quantity to be prorated (e.g., the number of TC4
otter trawlers absent more than 250 days in 1985) is distributed in the
population (i.e., all trips in the weighout data base) the same
as those in the sample (i.e., all trips in the interview data
base). Also, an additional assumption about the relationship between
effort and some known quantity, such as landings, must be made in order
to estimate the unknown quantity of effort associated with the noninterviewed
trips. Such assumptions could not avoid bias as implied in the
earlier discussion of that subject (e.g., larger otter trawlers
landing at principal ports are more likely to be interviewed, and the
effort- and location-based statistics for these vessels are more likely
to be accurate). Such assumptions could nonetheless be made.
Days Absent
The number of days absent by a fishing vessel was selected as the measure
of overall fishing activity instead of the number of days fished. The
number of days absent is a more robust measure since it is based on the
simple departure and arrival dates of the vessel from its home port,
and is, therefore, readily determined for vessels which are not often
interviewed. While the more restrictive days fished statistic is
usually considered a better measure of fishing effort for determining
fishing mortality, the days absent statistic is a better measure of annual
vessel activity.
To measure LPUE consistently, days fished must be adjusted for changes
in technology such as increased horsepower, larger nets, and more sophisticated
electronics and deck layout, all of which have increased fishing power
over time. Days absent may also be affected by these factors since,
for example, greater efficiency may result in shorter trips. Such
a tendency might, in turn, be offset by the ability to complete more
trips per year. In the case of declining resource abundance, however,
an increase in the number of days absent may be a consequence of needing
to remain at sea longer due to reduced ability to locate and/or catch
fish.
Statistical
Areas
The variable that defines the number of statistical areas in which a
vessel fished (Figure 1), which was chosen
to represent the locations fished, is one of four location variables
encoded on the weighout record: 1) 10 min of longitude by 10 min of latitude,
2) 30 min of longitude by 30 min of latitude, 3) NMFS statistical areas,
and 4) Northwest Atlantic Fisheries Organization (NAFO) subareas and
divisions. Each of the four variables represents an increasingly
broader level of spatial resolution, respectively. The 10-min square
areas are only encoded for interviewed trips, and would, therefore, require
proration of the noninterviewed trips in order to be used comprehensively. The
30-min square areas, the NMFS statistical areas, and NAFO subareas and
divisions are encoded for all trips, whether interviewed or not.
On noninterviewed trips, the statistical area is assigned by the port
agent based on a vessel’s recent activity pattern; however, statistical
areas are drawn on a sufficiently large spatial scale so as to minimize
judgment errors. Nevertheless, it is more likely that multiple
areas will be encoded on an interviewed trip (defined as a “split” trip)
than on one that is not interviewed.
Data Base Coverage
Over the 1980s, the voluntary data collection system grew to cover more
states and ports. Some new questions were added to the sampling
process, but the fundamental sampling design did not change. Essentially,
the system had been set up to collect information on biomass removed
by gear type from different fishing areas; it did not focus on individual
vessels.
One obvious limitation of the system was the omission of data on vessels
under 5 GRT. Landings data from these smaller vessels were recorded,
but were lumped under a general category of “unknown:under-tonnage.” Another
limitation was the lack of accurate reporting of the number of crew members
for a trip. The number of berths on a vessel was used as a proxy
for crew size. Another limitation was that there were more vessels
which fished in a given year than could be individually identified through
the weighout system. The federal fishing permit process which issues
permits to vessels fishing for regulated species didn’t help in this
instance because not all vessels with permits fished for the permitted
species, and some vessels were without permits since they fished for
unregulated species or in state waters only. Lastly, and importantly,
vessel cost information was difficult to obtain through the system.
Then, in 1994, requirements for federal fishing permits and logbooks
changed. Amendment 5 to the Fishery Management Plan for the Northeast
Multispecies Fishery requires annual permits for vessels, operators,
and dealers, and mandatory logbooks for fishermen. The logbooks
request data on several aspects of fishing activity. The value
of the information derived from the logbooks will still depend, however,
on the willingness of vessel captains to report data thoroughly and accurately,
and on the ability of the NMFS Northeast Region to process the data effectively
and efficiently.
The logbooks are designed to address concerns of universal coverage
and the practice of lumping catches. They should alleviate the
problem of multiple entries, reveal the number of vessels fishing in
a given year, and indicate which vessels fished part-time, were transients,
or didn’t fish a complete year due to different causes. At the
very least, the logbooks should enhance measurement of nominal fishing
activity (e.g., number of trips, time at sea) for all vessels. It
remains to be seen, however, whether information will improve on areas
fished. They will also have the potential for picking up some additional
data which can help in estimating cost information.
CONCLUSIONS AND RECOMMENDATIONS
Fisheries managers and policy analysts lack knowledge of key aspects
of the behavior of the Northeast otter trawl fleet. These key aspects
often involve the decision-making behavior of individual vessels, especially
in response to changes in fisheries management regulations.
This study has been a first parsing of the data collected through the
pre-1994, voluntary collection system in order to examine individual
vessel behavior. It has pointed out some surprising behavior patterns
for individual vessels. Although some of this behavior revealed
by the study appeared odd because of the methods used, other behavior
appeared that way because of real variation in the decision making by
individual vessels.
To improve the usefulness of the information emanating from future individual
vessel behavior studies, several steps should be taken. First,
attention will need to be given to new problems created by the mandatory
reporting requirement, such as reporting compliance and verification. The
introduction of bias into existing data bases should also be avoided
as much as possible when mandatory data are merged with, or are used
to prorate, the voluntary data.
Second, there is a need to examine the individual vessel behavior in
fisheries other than the otter trawl fleet.
Third, creating a multiyear analytical data set on individual vessel
behavior will require the use of front-end software capable of manipulating
data and testing hypotheses. In particular, such software should
be able to identify vessels fishing in or relocating to other regions
during the year.
Fourth, because of the value of having individual vessel behavior information,
the design of future data collection schemes and data base management
systems must incorporate the flexibility to create and examine individual
vessel data.
This approach of examining individual vessel behavior holds much promise
of revealing useful information to fisheries managers and policy analysts. Further
efforts, as noted above, should now be made to ensure that the process
of examining individual vessel behavior becomes more realistic.
ACKNOWLEDGMENTS
The
author acknowledges the assistance of the original members of the Fleet
Modelling Group who consisted of Anne Lange, Phil Logan, Ralph Mayo,
Tom Polacheck,
and John Walden.
REFERENCES
CITED
Conservation and Utilization Division,
Northeast Fisheries Science Center. 1993. Status
of fishery resources off the northeastern United States for 1993. NOAA
Tech. Memo. NMFS-F/NEC-101; 140 p.
Fisheries Statistics Division [, National Marine Fisheries Service]. 1993. Fisheries
of the United States, 1992. NMFS Curr. Fish. Stat. 9200;
115 p.
Halliday, R.G.; Pinhorn, A.T. 1997. Policy frameworks. In:
Boreman, J. Nakashima, B.S.; Wilson, J.A.; Kendall, R.L., eds. Northwest
Atlantic groundfish: perspectives on a fishery collapse. Bethesda,
MD: American Fisheries Society; p. 95-109.
Acronyms |
GRT |
= |
gross registered tons |
IVTS |
= |
individual vessel time series |
LPUE |
= |
landings per unit of effort |
NAFO |
= |
Northwest Atlantic Fisheries Organization |
NEFMC |
= |
New England Fishery Management Council |
NEFSC |
= |
Northeast Fisheries Science Center |
NMFS |
= |
National Marine Fisheries Service |
SA |
= |
statistical area |
TC |
= |
tonnage class |