Statistics

Spiny Lobster Update Assessment Review Workshop Report [1] by the Spiny Lobster Assessment Workshop provided the outputs and results from the stock assessment model. Those results and outputs evaluate the stock condition. In this page, we will present to you some selected statistic data and results.

Reported landings (thousand pounds) of the Caribbean spiny lobster in the western central Atlantic, 1950-2008. (Source: FAO Fisheries and Aquaculture Statistics and Information Service. 2010.).

Commercial landings in pounds by gear and fishing year for spiny lobster off the Southeastern Unites States.

Commercial, recreational, total landings, and percent recreation landings by fishing year.

These three data sets show the landing statistics of the spiny lobster. We can see in general, the landing of the spiny lobster is increasing with the year. The majority of the landing comes from commercial harvest, while recreation harvest occupies about 20% of the total landing.

In SEDAR, two statistical assessment models have been applied to evaluate the spiny lobster stock condition. The primary assessment model was the Integrated Catch-at-Age (ICA) model, while a Modified DeLury model was considered secondary and used to provide a comparison of model results. In this section, we present and compare the results of these two models.

ICA: ICA is a composite of a separable virtual population analysis and sequential population analysis. In this analysis, we use age to classify the stock.

Modified DeLury model: This model view population as one unit of biomass, with all individuals having the same growth and mortality rates, no age structure exists in this model. The population only increases by recruitment and is decremented by total mortality.

Fishing Mortality:

Modified DeLury:

Fishing mortality per year by fishing year for the recreational fishery (blue bars), commercial fishery (yellow bars), and attractant fishery (black bars).

Average fishing mortality rates (ages 1 – 5) estimated by ICA. The vertical line is the 95% confidence interval, the box is the inter-quartiles (25 to 75 percentiles) and the horizontal line is the median.

ICA:

Comparison:

Comparison of the fishing mortality rates from the selectivity adjusted DeLury model and the age-structured model ICA.

The DeLury model predicts an overall higher fishing mortality than the ICA model. In the ICA model, the fishing mortality was overall stable from 1985 to 2007 (bounce around 0.5), then it decreased after 2007. In the DeLury model, the trend is similar. However, the fishing mortality increased and decreased more dramatically. Also the fish mortality is higher around 1.

Biomass:

ICA:

Modified DeLury:

Biomass of lobsters at the beginning of the fishing year.

Total biomass and spawning biomass in Southeast US by fishing year. The vertical line is the 95% confidence interval, the box is the interquartiles (25 to 75 percentiles) and the horizontal line is the median.

The trends of the biomass are similar in both models: the biomass reached the lowest around 2010 and then slightly increased. However, the ICA has a higher in biomass estimation.

Biological Reference points:

We choose Static spawning potential ratio (SPR) as the biological reference point. Overfishing was defined as a fishing mortality rate (F) in excess of the fishing mortality rate at 20% static SPR (F20%). Static SPR is the equilibrium value associated with any particular fishing and natural mortality rates, selectivity, maturity, and biomass [2].

Static spawning potential ratios by fishing year (established using the assumed and estimated maturity schedules) and the current management objective of 20%.

From the result, we can see the stock is not currently overfishing.

Reference:

[1] Southeast Data, Assessment, and Review 8 (SEDAR 8). 2005. Stock Assessment Report III, Southeastern US Spiny Lobster, Section III, Assessment Workshop, Assessment of spiny lobster, Panulirus argus, in the southeast United States. Stock Assessment Report prepared by SEDAR 08 U.S. Stock Assessment Panel. Available from http://www.sefsc.noaa.gov/sedar/Sedar_Workshops.jsp?WorkshopNum=08%20B

[2] Mace, P., L. Botsford, J. Collie, W. Gabriel, P. Goodyear, J. Powers, V. Restrepo, A. Rosenberg, M. Sissenwine, G. Thompson, and J. Witzig. 1996. Scientific review of definitions of overfishing in U.S. fishery management plans, Supplemental Report. National Marine Fisheries Service.