Relationship between variations in sea bottom temperature and American lobster catch rate off southwestern Nova Scotia during 2008–2023

Abstract

Abstract. American lobsters (Homarus americanus) are an iconic species and are the socioeconomic and cultural mainstay for many communities across Nova Scotia. Describing the changes in population biomass and providing annual stock assessment advice for this species are required for sustainable fisheries. In many areas the best information available for providing this advice comes from commercial fishery data. Often there is an assumed relationship between fishery performance (catch per unit effort; CPUE) and available biomass; however several studies indicate that this relationship can be affected by external factors such as sea bottom temperature. Including bottom temperature when developing a standardized CPUE index will potentially address these concerns; however it has proven difficult in the past due to the lack of readily available (near-real-time) and unbiased bottom temperature data at the spatial and temporal scales required. Here we explore a global ocean reanalysis product of the European Union Copernicus Marine Service with an application to the fishery catch data from Lobster Fishing Area 33 during 2008–2023. A comparison with observational data shows that this reanalysis product provides realistic variations in sea bottom temperatures in this region. Next, a hierarchical generalized linear modelling approach is applied to evaluate the relationship between within-season changes in lobster CPUE and sea bottom temperature. Positive relationships between the rates of change of two model parameters, during the first 60 d of the fishing season (from mid-November to mid-January), are found in the majority of the 10 subregions. A standardized CPUE index with the influence of bottom temperature included, compared to the index without such influence, explains a high percentage of the deviance of CPUE data and hence is more consistent with available stock biomass. The outcomes of the model evaluation and relationship analysis encourage further applications of multi-decadal ocean reanalysis products to understand past changes, as well as the development of ocean forecasts for predicting future changes in marine ecosystems and fisheries, a product with wide-reaching socioeconomic value.