Consistent with the California Marine Life Management Act, a fishery management plan (FMP) is being developed for the state’s spiny lobster fishery to help sustain it over the long term. The FMP requires identification of suitable protocols for collecting data, as well as the best available scientific information to inform management. The main source of information currently available to fishery managers is the commercial logbook and landing receipts. These sources of data allow managers to determine three reference points used to gauge the health of the fishery: catch, catch per unit effort (CPUE) and spawning potential ratio (SPR). The fishery is currently managed as a single area, but given the different habitats and environmental conditions occurring in the Southern California Bight, fishery parameters may vary biogeographically. To explore spatial trends within the California spiny lobster commercial fishery and how these may affect management, I analyzed three years of essential fisheries information collected through a collaborative at-sea sampling program (CASP), where commercial fishermen collect data on their catch while conducting their day-to-day fishing activities.
My analyses of CASP data identified significant spatial patterns in lobster size distributions, biomass per trap, sex ratios, reproductive output, and the number sub-legal lobsters for three regions; South, North Coast and North(west) Islands. The majority of lobsters harvested in the South were small, averaging 86 mm among years, representing recent recruits to the fishery as they are just over legal size (82.5 mm). Given the small legal size and high fishing effort in this region commercial fishing may be near its maximum exploitation rate there. Unlike the South, legal lobster in North Coast and North(west) Islands are much larger averaging 90 mm and 97 mm among years respectively. The larger legal size and the lower fishing effort in these regions suggest commercial fishing may be below the maximum exploitation rate there. While the South may have a high exploitation rate, this region had significantly more sub-legal lobster (i.e., potential future recruits) compared to both the North Coast and North(west) Islands, which may help to mitigate the high exploration rate. Further, in the second year, sex ratios of legal lobster indicated a slight trend toward higher removal of female lobster in the North Coast (56:44) and North(west) Islands (64:36) regions as compared to the South (47:53), suggesting higher trap vulnerability and potentially decreased reproductive capacity in those two regions. Sub-legal sex ratios were female biased (>60%) in all regions for most years, suggesting additional impacts to trap vulnerability and reproductive capacity. Lastly, assessments of reproductive capacity suggest that egg production per trap is greatest in the South (408,000 eggs per trap) compared to both the North Coast (166,000 eggs per trap) and North(west) Islands (112,000 eggs per trap). This finding is influenced by the large number of mature sub-legal lobsters that will remain in the population in the South.
The essential fisheries information (EFI) collected by the CASP augments existing CDFW management data and can be used to inform two of the three reference pointed being considered for the FMP; CPUE and spawning potential ratio (SPR). My comparisons of CASP and CDFW data identified several shortcomings with commercial logbook and landings data. First, fishermen may estimate the number of trap pulls for the commercial logbook, which affects the accuracy of the CPUE reference point, while CASP data is recorded per trap providing an accurate count of the number of traps. Logbook data also contain many erroneous and missing entries that are time consuming to filter out. Second, issues with correlating logbook to landing receipt data affects the calculation of average weight, which is used in fishery models to determine the SPR reference point. I determined that the average weight from logbook/landings data was similar to that calculated from CASP data for the South and North Coast. However, average weight determined from the logbook/landings for the North(west) Islands was larger than CASP data; correlating to 114 mm and 97 mm carapace length respectively. Other studies support the findings of the CASP data. Given these issues, CASP data may be more efficient, accurate and cost-effective for informing management on the status of the fishery.
Overall, the regional variation in catch characteristics suggests area-based management may be more appropriate for the California lobster fishery. Further, the current model used to determine SPR reference point should consider the abundance of sub-legal lobsters and higher trap vulnerability for female lobsters, as it impacts the reproductive capacity of each region thereby warranting the continued collection of size and sex data. The demonstrated utility of the pilot CASP program for collecting fishery-dependent EFI across the entire range of the fishery, along with the critical need for such data as identified by a recent scientific review of the FMP, has generated support for implementing an ongoing CASP program to inform long-term management of the lobster fishery.
