Relationship between Chilean hake (Merluccius gayi gayi) abundance and environmental conditions in the central-southern zone of Chile

The Chilean hake (Merluccius gayi gayi) is one of the most important demersal resources fished in Chile since the early 1940s. Since 1993, an acoustic survey program was established to assess the abundance of this resource. A sudden decrease in abundance was observed after 2002, along with changes in the species demography and spatial distribution. These changes represent a spatial re-distribution of the stock (latitude, longitude, and depth) which was associated with concomitant changes in environmental conditions (temperature, salinity, and dissolved oxygen). The main aim of this paper is to determine habitat preferences in Chilean hake and associated changes in its abundance with environmental conditions. Estimates of Chilean hake abundance were based on acoustic survey conducted between 1993 and 2006 from Coquimbo (29°30′S) to Chiloé Island (41°28.6′S). Chilean hake abundance was modelled using generalised additive models with environmental variables and location as covariates. In the interannually analysis, location and temperature were the most important explanatory covariates of Chilean hake abundance. Analyses of the data across years revealed that time, Chilean hake aggregation depth, and temperature were the most important covariates. The changes observed in spatial distribution can be divided into two periods. During the first period (1993–2001) high values of Chilean hake abundance were found in salinities between 34 and 34.4 psu, temperatures of 8 and 11 °C, and depths between 125 and 400 m. During the second period (2002–2006) the stock increased in the southernmost area closer to the coast and were associated with low salinities (<34 psu). In this paper we discuss the spatial and temporal changes in Chilean hake abundance, their habitat preferences, and how the association between abundance and environmental variables changes during these periods of high and low abundance.