Does one size fit all? An evaluation of length-weight relationships for New Zealand's freshwater fish species

Length-weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length-weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length-weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length-weight relationships was also assessed. Location, in particular, generated different length-weight relationships for 65% of the species examined. Length-weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R-2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand.