2001 East Coast Weakfish Stock Assessment

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An update of the stock assessment and status of
Florida east coast weakfish, Cynoscion regalis

Janaka A. de Silva and Robert G. Muller
Florida Fish and Wildlife Conservation Commission
Florida Marine Research Institute
St. Petersburg, FL
August 29, 2001

EXECUTIVE SUMMARY

Estimated total landings of weakfish in 2000 were higher than 1999 (153,000 pounds vs. 134,000 pounds). The recreational harvest accounted for 94% of landings and has increased both in number and proportion since 1999, when it accounted for 87% of landings.

Preliminary estimates for 2000 indicate that the commercial fishery harvested 9,360 pounds in 639 trips. Commercial weakfish landings in 2000 were 47% lower than 1999 landings, with 37% fewer trips being made in 2000.

In 2000, an estimated 161,161 weakfish, weighing 143,265 pounds were harvested (Type A1+B1 +0.2B2) by recreational fishers. In terms of weight, the recreational harvest of weakfish in 2000 was the second highest during the last fifteen years. When comparing 2000 landings to 1999 by numbers of fish, the harvest was 13% higher than 1999 and 23% higher in terms of weight. Using standardized trips as an estimate of recreational effort, the number of trips during which weakfish were harvested increased by 45% over 1999 estimates.

Based on the preliminary catch estimates, the total harvest of weakfish in Florida was 1.20% of the 1999/2000 average coastwide landings. However, given the variability associated with the estimated recreational landings (represented by PSE) the estimate of Florida's weakfish harvest is not likely to be significantly different from the 1% de minimis criteria.

Examination of recreational length frequencies indicates that the 12-inch minimum size that was implemented in 1994 has had little effect on the size of fish landed. The average percentage of weakfish less than 12 inches in the recreational sector prior to the minimum size was 28% (CV = 54%) and 24% (CV = 66%) after its implementation. For the commercial sector, an average of 30% of weakfish (CV = 103%) were less than 12 inches before the 12-inch minimum size was implemented and an average of 31% (CV = 70%) were undersized afterwards.

To evaluate the efficacy of the bag limit, recreational intercepts were grouped into two time periods representing pre- and post-regulations: 1982-1994 and 1995-2000. The standard bootstrap model was run on intercepts from each of the periods. Based on the results of the bag limit analysis, 4.4% of trips exceeded the 4 fish bag limit during the post-regulatory period. Furthermore, the analysis also indicates that the bag limit has reduced the recreational harvest by about 13%, which is about half of the expected reduction.

Estimates of weakfish fishing mortality rates (F) and population size from 1986 to 2000 were made using a similar protocol to that used in the 2000 assessment. For 2001, Integrated Catch-at-Age Analysis which is a separable virtual population analysis was used. While the general methodology used in the 2001 assessment was similar to 2000, three changes were made in the data used in the analysis. In addition, one of the assumptions made in the analysis was also changed.

Population size estimates showed that the number of weakfish on Florida's Atlantic coast increased from 803,610 in 1986 to 1,072,840 in 1993. From 1993, population estimates declined to a low of 308,640 weakfish in 1996 during the period 1986-2000. Population estimates in 1997 were 387,900 and increased to 594,520 fish in 2000.

From 1986 to 1993, estimates of fishing mortality rates (F) for ages 1-5 were variable, fluctuating around an average F of 1.27 per year. In 1994 the fishing mortality rate abruptly increased to 1.98 per year and has declined following the implementation of the 1995 Constitutional limit to net fishing, minimum size, and bag limit. While estimates have varied since 1995, recent estimates of F for 1999 and 2000 were 1.21 per year (95% confidence interval 0.89-1.60) and 1.39 per year (95 % confidence interval 0.77-2.58) respectively. While previous assessments indicated that fishing mortality estimates for Florida weakfish had been below the yearly ASMFC target values since 1996, this assessment indicates that the 2000 ASMFC target of 0.50 has been exceeded.

Comparing the population size and fishing mortality estimates from the present assessment to those in the 2000 assessment indicated that population estimates follow a similar trend. However, for the terminal years in the analysis (1998 and 1999) estimates based on the 2001 assessment indicate lower population and higher fishing mortality estimates, particularly for 1999, than do those in the 2000 assessment. Discrepancies in population estimates and F values in the terminal year are most likely related to the methodology, which is sensitive to terminal F values that enable the analysis to be extended to incomplete cohorts, and the model specifications used in the current analysis.

The primary area for improving the analysis is obtaining better age information. While the recreational fishery for weakfish has grown in importance and now accounts for 95% of the harvest, the biological information that is used in the age analysis is derived primarily from commercial sources. Weakfish for age analyses need to be collected from all aspects of the fishery.

For other information:
Stock assessments for finfish and invertebrate
Weakfish species account.

Prior to July 1, 2004, the Fish and Wildlife Research Institute was known as the Florida Marine Research Institute. The institute name has not been changed in historical articles and articles that directly reference work done by the Florida Marine Research Institute.