Black sea bass, Centropristis striata,
are distributed in the Northwest Atlantic from Maine to Florida
(Figure
16.1) with Cape Hatteras, NC serving as a geographic boundary
between northern and southern stocks (Musick and Mercer 1977,
Shepherd 1991). Sea bass are members of the family Serranidae,
which includes groupers commonly found in tropical and sub-tropical
waters. Structures such as reefs, wrecks or oyster beds are preferred
habitats.. Black sea bass may attain sizes up to 60 cm (23.5 in)
and 3.6 kg (8 lbs) with maximum age of 10-12 years. Sexual maturity
is attained between ages 2 to 4 for females. Black sea bass are
protogynous hermaphrodites, meaning that they change sex from
female to male. Born as females, most fish will change sex to
males between ages 2 to 5 (Musick and Mercer 1977). The factors
that lead to the sex change have not been proven although it has
been speculated that the relative scarcity of males in a spawning
group may be the stimulus for a female to switch sex. Spawning
in the northern stock generally occurs from April to June after
fish have migrated into coastal habitats (Collette and Klein-MacPhee
2002).
Males develop a pronounced
blue hump on their heads during spawning season and aggressively
defend territory although actual spawning behavior is not well
documented. Larvae and juveniles develop and grow in inshore habitats
and juveniles attain lengths of 10-14 cm by fall. Sea bass remain
in coastal habitats until water temperatures decrease in fall
into early winter, and then migrate to deeper offshore water along
the edge of the continental shelf. In the spring, most fish return
to the same area that was vacated the previous fall. Juvenile
sea bass experience little if any growth throughout the winter.
Adult black sea bass are omnivorous, feeding on a variety of benthic
invertebrates, squid and fish (Steimle et al.1999).
Black sea bass are jointly managed under the
Summer Flounder, Scup and Black Sea Bass Fishery Management
Plan developed jointly by the Atlantic States Marine Fisheries
Commission (ASMFC) and the Mid-Atlantic Fishery Management Council
for the commercial fisheries involves annual quotas, size limits
and gear restrictions, while the recreational fisheries are
controlled by size and bag limits.
The Fishery
Total recreational landings in
2005 were 787 mt, similar to the 2004 estimate of 760 mt (Table
16.1,Figure
16.2[Fig
16.2 Data]) and a substantial decrease from the 2002 landing
of 1,987 mt and below the 1981-2004 average of 1,700 mt. Recreational
fisheries over the past decade have accounted for 50% of the total
landings, by weight. The recreational fishery generally occurs in
coastal areas from May until November and is presently subject to
a 12” (30 cm) minimum size and a 25 fish bag limit. In 2004-2005,
65% of the recreational landings were from the state of New Jersey,
11% from Delaware, and 9% from Maryland. The average length of sea
bass in recreational landings in 2005 was 34 cm. Black sea bass
discards in the recreational fishery amounted to 5.7 million and
5.8 million fish in 2004 and 2005, respectively. The highest estimates
of discards occurred during 2000-2002 when the discards ranged between
11.6 million and 13.2 million fish. As with landings, New Jersey
accounts for the largest percent of discards.
Commercial fisheries occur
in two distinct seasons; a spring through fall inshore fishery,
and a winter offshore fishery. The inshore fishery is prosecuted
primarily with hook and line and pot gear. Since 2000, these gears
have accounted for 11% and 37%, respectively, of total commercial
landings. Commercial landings in 2005 were 1,310 mt, only slightly
less than in 2004 and 2003 (Figure
16.2[Fig
16.2 Data]). ). By comparison, landings in 1952 were nearly
10,000 mt, but declined to 566 mt by 1971 (Figure
16.3[Fig
16.3 Data]). Since 2000, NJ, VA and MA have together
accounted for 60% of black sea bass commercial landings. The average
length of sea bass in commercial landings in 2005 was 35 cm. Since
2000 commercial discard estimates have ranged from 33 mt to 202
mt but these values are likely conservative estimates.
Figure 16.2
Figure
16.3
Figure 16.4
Figure 16.5
Figure 16.6
Research
Vessel Survey Indices
NEFSC survey indices from the
spring and winter offshore survey in the Middle Atlantic are used
to index abundance since the fish are most vulnerable to trawl
gear during this season. NEFSC spring abundance indices for adult
sea bass (loge retransformed stratified mean number
per tow for fish > 22 cm) have varied considerably since the
beginning of the time series in 1968 (Figure
16.4[Fig
16.4 Data]). Indices between 1968 and 2001 averaged
0.39 fish per tow, with the exception of 1974 (with a mean value
of 1.23 sea bass per tow). The index increased to 1.25 and 1.61
fish per tow in 2002 and 2003, respectively, but declined to 0.46
fish per tow in 2006. Abundance indices of juvenile sea bass (loge
re-transformed stratified mean #/tow for fish <14 cm) in both
the winter and spring surveys indicate large 1999 and 2001 cohorts
(Figure
16.5[Fig
16.5 Data]). In both surveys, the 2005 cohort appears
below average.
Assessment Results
Uncertainty in the results of a recent tagging
study prevented determination of current fishing mortality ( NEFSC
2006b). However, survey biomass indices suggests that the relative
exploitation (catch weight from fisheries/survey index of fish biomass
of exploitable sizes) of black sea bass has been below the time
series average (Figure
16.6[Fig
16.6 Data]) but increasing in 2005. The NEFSC survey
loge re-transformed biomass indices peaked at 0.62 kg
per tow but subsequently declined through 2006. The 2006 biomass
index (0.29) remains above the times series average of 0.17 kg per
tow. Landings in the commercial fishery have remained stable while
recreational landings have recently declined.
Biological Reference Points
(Fmax = 0.33) (Figure
16.7[Fig
16.7 Data],Table
16.2) is used in the FMP as a proxy for Fmsy. However, there
are no estimates of current fishing mortality to evaluate to this
reference point. The biomass reference point defined in the FMP
is based on average NEFSC survey biomass indices for 1977-1979.
However, a recent scientific review of that reference point concluded
that it was not suitable as a basis for determining stock status.
Alternative measures are currently being explored.
Summary
Total black sea
bass landings have been relatively stable over the past decade despite
recent declines in recreational landings. Adult survey abundance
indices increased in 2002 and 2003 but have recently declined to
average levels. The appearance of several recent strong year classes
in recent years has likely contributed to the spikes in adult abundance.
The current status of the stock relative to biological reference
points cannot be determined at this time.
Collette, B.B. and G. Klein-MacPhee
(ed.). 2002. Bigelow and Schroeder’s Fishes of the Gulf of
Maine. 3rd edition. Smithsonian Inst. Press. Washington, D.C. 748
p.
Musick, J. A. and L. P. Mercer.
1977. Seasonal distribution of black sea bass, Centropristis
striata, in the Mid-Atlantic Bight with comments on the ecology
of fisheries of the species. Transactions of the American Fisheries
Society 106(1):12-25.
Shepherd, G.R. 1991. Meristic and morphometric variation in black
sea bass north of Cape Hatteras, North Carolina. North American
Journal of Fisheries Management. 11:139-148.
Steimle, F.W., C.A.Zetlin, P.L. Berrien
and S. Chang.1999. Essential Fish Habitat Source Document:
Black Sea Bass, Centropristis striata, life history
and habitat characteristics. NOAA Technical Memorandum NMFS-NE-143.