Comparison of lethal and non-lethal age-based growth estimation methodologies to assess an endemic bay population of Atlantic cod (Gadus morhua)

Abstract

The Gilbert Bay, Labrador, MPA (Marine Protected Area) was created in 2005 to protect a genomically distinct and locally adapted bay resident population of Atlantic cod (Gadus morhua) from commercial overfishing. Since then research showed that significant numbers of individuals migrate beyond MPA boundaries creating a concern that fishing continues to impact this endemic population. As part of research and MPA monitoring to assess the health of the protected cod population, lethal sampling of Gilbert Bay cod was conducted from 1998 to 2009 to gather length-at-age data from otoliths. Since then only non-lethal sampling methods were used so as to help conserve the protected population. This study was conducted to compare non-lethally (mark-recapture and length-frequency) obtained age and growth data with lethally (otolith-length-at-age) obtained data. The three methods produced similar results for the 1998 to 2009 period, and both of the non-lethal methods considered were consistent over the 20 year study, confirming their preference over lethal methods for this small endemic fish population.