Environmental associations of Pacific bluefin tuna (Thunnus orientalis) catch in the California Current system

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 somewhat 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.

Flexible use of a dynamic energy landscape buffers a marine predator against extreme climate variability

“…Our findings that juvenile Pacific bluefin tuna migrate flexibly in response to climate variability and maintain a high energy intake under anomalously warm ocean conditions have important implications for managing this population. Bluefin tuna fisheries operating in the California Current have seen a recent rise in catches, including during the 2014–2016 marine heatwave [57]. These increases in catch rates do not appear to be related to an increase in stock biomass, which remains at near-historic lows with less than 5% of the population remaining [24].…”

“…These increases in catch rates do not appear to be related to an increase in stock biomass, which remains at near-historic lows with less than 5% of the population remaining [24]. Instead, these changes appear to represent an increase in the presence of larger bluefin tuna in the California Current potentially due to changes in the distribution of suitable habitat or the availability of key prey species [57]. Climate change is expected to increase temperatures and decrease productivity in much of the California Current [45], potentially leading to shifts in the seasonal migrations of juvenile Pacific bluefin tuna which may affect their availability to commercial and recreational fisheries in Mexican and US waters.…”

Spatial Distribution, Temporal Changes, and Knowledge Gaps in Basking Shark (Cetorhinus maximus) Sightings in the California Current Ecosystem

“…To account for the strong class imbalance due to the large proportion of absences, we up-sampled the training data such that presences represented 8% of the dataset (versus ∼1.5% before up-sampling). We assessed model skill using the Area Under the Receiver Operating Characteristic (ROC) curve: (AUC) (Hanley and McNeil, 1982;Runcie et al, 2019). The AUC metric varies between 0 and 1, with a value of 0.5 indicating that the model predictions were no better than random, and a value of 1 indicating that the model is capable of distinguishing presences and absences perfectly (Elith et al, 2006;Parisien and Moritz, 2009;Runcie et al, 2019).…”

Fisheries Surveys Are Essential Ocean Observing Programs in a Time of Global Change: A Synthesis of Oceanographic and Ecological Data From U.S. West Coast Fisheries Surveys

“…Humpback whales (Megaptera novaeangliae) were closer to shore than usual, likely to feed on anchovy, which caused more whale entanglements in Dungeness crab (Metacarcinus magister) fishing gear, greater whale mortality, and intermittent fishery closures (Santora et al, 2020). Catch of Pacific Bluefin tuna (Thunnus orientalis) by the commercial passenger fleet off California was very high, as tuna associated with warm water and foraged on anchovy (Runcie et al, 2019). Seabird population dynamics differed during and after the marine heatwave depending on prey needs.…”