Quantify the effects of commercial Dungeness crab fishing on the Glacier Bay marine ecosystem

INVESTIGATORS: Taggart, Spencer J.; O'Clair, Charles E.; Shirley, Thomas C.

PROJECT DESCRIPTION:
This project will measure the effects of the large scale fishing closure on the Dungeness crab population structure and catch per unit effort (CPUE). The purpose is to characterize the size and structure of the Dungeness crab population at selected sites in Glacier Bay before and after the closure of the fishery. In addition to estimates of population density and descriptions of size distributions of crabs, we will characterize the physical condition of individual crabs and the reproductive condition of female crabs during the brooding period. The pre-closure studies are essential, as they will provide baseline information that will be critical for interpreting the results of the post-closure studies. Extensive commercial fisheries began before Glacier Bay National Monument, Alaska was established in 1925 (Taylor et al. 1990). Glacier Bay was designated a National Park by the Alaska National Interest Lands Conservation Act of 1980 (U.S. Congress 1980). The Omnibus Consolidated and Emergency Supplemental Appropriations Act for Fiscal Year 1999 immediately closed parts of Glacier Bay National Park to commercial fishing, directed others parts to close after the lifetime of qualifying fishermen, and left some parts open to continued commercial fishing. The duration of the phase out is likely to be decades. The Dungeness crab fishery was one of the fisheries that was closed completely in Glacier Bay proper in 1999. Closures of crustacean fisheries are usually prompted by major declines in the abundance of the harvested species; the result is that the fishery usually collapses (Kruse 1993; Orensanz et al. 1998). Such closures normally remain in effect only until there is evidence that the fished stocks are rebounding. By closing commercial fishing in parts of the Glacier Bay National Park, the NPS is effectively creating permanent marine reserves. During the 1990's, collapsing fisheries around the world have caused doubt about the long-term sustainability of certain fisheries. There is an emerging theoretical and empirical body of information that hypothesizes that "no-take marine reserves" could enhance the long-term sustainability of many fisheries and marine biodiversity (Ballantine 1991; Ballantine ; Ballantine 1992; Bohnsack 1996; Breen 1988; Chisholm 1993; Dugan et al. 1993; Eldredge ; Folk 1996; Guenette et al. 1998a; Guenette et al. 1999; Guenette et al. 1998b; Kenchington 1989; Kennedy 1990; Pitcher 1997; Polunin et al. 1993; Roberts 1994; Roberts et al. ; Roberts et al. 1993; Rogers-Bennett et al. 1995; Russ 1996; Sobel 1996; USGS 1996; Van Dyke 1991; Ward et al. 1999). Although theoretical concepts and simulation models are rapidly being developed for marine reserves, their effectiveness has been demonstrated primarily in tropical areas; data from high latitudes are extremely limited. Quantitative records of the Dungeness crab fishery start in 1970. Between 1970 and 1995 the harvest for Glacier Bay and Icy Strait (114) has ranged from 76,000 to 658,000 pounds (Koeneman et al. 1995). Recent increases in Dungeness crab harvests in southeastern Alaska have resulted in the capture of a large proportion of the legal stock (Koeneman 1985). High exploitation rates coupled with reductions in escapement under the sex and size regulations presently in force result in a decrease in the maximum size of males in the population toward the legal size limit. Release from human exploitation by closure of the fishery should, over time, result in a shift in the crab population to larger males. Because males clasp smaller females during mating (Snow et al. 1966), an increase in the abundance of large males may result in a greater probability of successful fertilization of the eggs of large females. A consequence might be an increase in the relative abundance of ovigerous vs. non-ovigerous large females and perhaps an increase in the percentage of fertilized eggs in the clutches of large females. This assumes that male size limits successful fertilization of the clutches of large females in the previously exploited population. In 1992 we took the initiative to begin collecting preclosure data on the Dungeness crab fishery in Glacier Bay National Park. Our study has continued on an annual and sometimes biannual basis since its inception in 1992 (see SIS 5001251). In 1999 and 2000 we collected our first post-closure data. A major criticism of many marine reserve evaluations is the scarcity of baseline data (Conover et al. 2000). Without baseline data it is difficult to determine the potential effects on a population after the closure of commercial fishing. In Glacier Bay we have the rare opportunity to compare changes in the structure of populations previously fished to populations that are now protected.