Not all fisheries dependent data tell the same story. Runcie et al. 2018 in Fisheries Oceanography shows how different fisheries and different gears show different preferences when fit with habitat models. It highlights an inherent difficulty in understanding the underlying habitat of a highly migratory predator from spatially restricted datasets.
Abstract: We investigate the impact of oceanographic variability on Pacific bluefin tuna (Thunnus orientalis: PBF) distributions in the California Current system using remotely sensed environmental data, and fishery‐dependent data from multiple fisheries in a habitat‐modeling framework. We examined the effects of local oceanic conditions (sea surface temperature, surface chlorophyll, sea surface height, eddy kinetic energy), as well as large‐scale oceanographic phenomena, such as El Niño, on PBF availability to commercial and recreational fishing fleets. Results from generalized additive models showed that warmer temperatures of around 17–21°C with low surface chlorophyll concentrations (<0.5 mg/m3) increased probability of occurrence of PBF in the Commercial Passenger Fishing Vessel and purse seine fisheries. These associations were particularly evident during a recent marine heatwave (the “Blob”). In contrast, PBF were most likely to be encountered on drift gillnet gear in some- what cooler waters (13–18°C), with moderate chlorophyll concentrations (0.5– 1.0 mg/m3). This discrepancy was likely a result of differing spatiotemporal distribution of fishing effort among fleets, as well as the different vertical depths fished by each gear, demonstrating the importance of understanding selectivity when building correlative habitat models. In the future, monitoring and understanding environmentally driven changes in the availability of PBF to commercial and recreational fisheries can contribute to the implementation of ecosystem approaches to fishery management.
Runcie, B. Muhling, E.L. Hazen, S.J. Bograd, T. Garfield, G. DiNardo, 2018. Environmental associations of Pacific bluefin tuna (Thunnus orientalis) catch in the California Current system. Fisheries Oceanography, doi:10.1111/fog.12418. PDF