Pelagic longline gear depth and shoaling

摘要: Temperature-depth recorders (TDRs) were attached to pelagic longline gear in the Hawaii-based commercial fishery obtain actual fishing depths and test accuracy of catenary algorithms for predicting depths. Swordfish was set shallow by typically deploying four hooks between successive floats. The observed depth settled deepest hook had a median value 60 m 333 swordfish sets. Tuna deployed more floats (mean = 26.8), 248 (n 266 sets). Maximum predicted from estimates sag ratio algorithms; however, not all TDR-monitored sets because estimating ratios proved problematic. less slack main line correspondingly smaller angles (median 54.2 ◦ ) than tuna 63.7 ). Median values 123 ( n 203) 307 198). Shallow reached only ∼50% their depth, while deeper about 70%. These indicated that capture using traditional equations may be biased without benefit TDRs affixed longlines. Generalized linear models (GLMs) generalized additive (GAMs) developed explain percentage shoaling as function environmental effects wind stress, surface current velocity, shear. GAM explained 67.2% deviance 41.3% Predicted always initial variable included stepwise process, inclusion information approach an additional 10–17% compared GLMs. explanatory ability data have been limited scale observations (1 space; weekly or monthly time) geometric (transverse versus in-line) forcing environment set. Longline with affecting improved future studies incorporating contemporaneous information, although this restrict analyses fine-scale experimental Published Elsevier B.V.