Community Based Fisheries Research on California Spiny Lobster (Panulirus interruptus) at the Santa Barbara Channel Islands
This dissertation describes collaborative fisheries research (CFR) on Californiaspiny lobster (Panulirus interruptus) at the Santa Barbara Channel Islands (SBCI).The research goals addressed in this work include: (1) establishing a collaborativeapproach to gathering fisheries data for assessments and management; (2)assessment of marine reserves at SBCI; (3) estimating mortality rates of lobsterspopulations throughout the SBCI marine reserve network; and (4) construction offisheries models that provide context for interpreting mortality rates I estimated.
CFR enhanced assessment of marine reserves established in 2003 at the SBCIin terms of their impact in P. interruptus population structure and fisheryinteractions. After six years of reserve protection, there was a four to eight-foldincrease in trap yield, a 5–10% increase in the mean size (carapace length) of legal sized lobsters, and larger size structure of lobsters trapped inside versus outside of three replicate reserves. Patterns in trap data were corroborated by visual SCUBA surveys that indicated a four to six-fold increases in lobster density inside reserves. These results indicate that marine reserves have strong conservation benefits for P. interruptus. Inside reserves, trap performance (the number and mean size of legal-sized lobsters caught in traps) was significantly influenced by proximity to reserve borders, a pattern that suggests net emigration of lobster from inside reserves to adjacent fished areas (spillover). Interestingly, spillover was not apparent in trap yields or commercial fishery effort distribution outside reserves, nor was it apparent in tagging studies. This suggests that spillover from reserves may have little influence of fishery yield outside reserves. However, yield due to spillover might increase as the reserves age and lobster biomass continues to increase inside reserves.
Mean total mortality (Z) of female lobsters was lower at sites inside reserves (Z= 0.21 [±0.07 SE]) than at sites outside reserves (Z = 0.59 [±0.02 SE]). Meanmortality at all sites inside reserves, and among sites near reserve centers (where Z= 0.17 [±0.05 SE]), was similar to estimates of natural mortality for other temperate spiny lobster species. Among sites inside reserves, there was a positive relationship between mortality and proximity to reserve borders, but this relationship was absent among sites outside reserves. Mortality estimates were much more variable among sites inside reserves than at sites in fished areas. Results of YPR models suggest that increased effort in this fishery will not resultin commensurate increases in yield. However, current spawning potential at SBCI is ~20% (of virgin conditions), and this could decrease with increased effort. Ourcollaborative framework provides a stable and inclusive framework for conductingfuture research that informs management of this fishery and fosters stakeholdersupport.