Accounting for Habitat-Dependent Observation Error in Bottom Trawl Survey Indices for Pelagic Stocks Using Butterfish (Peprilus triacanthus) as a model

Josh Kohut, Rutgers

Dynamic properties (e.g. temperature) and process (e.g. horizontal and vertical advection) of the oceans fluid primarily determined by atmospheric and climate forcing define important habitat features in the sea.  As a result marine habitats are spatially dynamic particularly for pelagic species which, in temperate latitudes, exhibit long distance migrations associated with seasonal changes in climate forced properties and processes. Changes in the seasonal phenology of habitats and migration with global climate change may result in systematic changes in proportions of habitat sampled during fishery independent surveys that are performed during specific calendar periods on continental shelves and which typically leave un- or under-sampled, shallow near-shore (depth < 15 M) and deep offshore habitats  (>240 M), as well as specific times of year.  Systematic changes in proportion habitat sampled from year to year could confound estimated trends in population size with spatial habitat dynamics.  We are assembling a collaborative working group of government and academic researchers and fishing industry experts to identify and model effects of changing climate on seasonal habitat dynamics and migration in butterfish, Peprilus triacanthus.  We will develop a method that uses dynamic habitat models to quantify habitat dependent observation errors in fishery independent survey indices of abundance and thereby reduce an important uncertainty in population assessments for pelagic stocks.