Working with community fishers to determine the spawning seasonality of two commonly targeted jack species

Abstract

Objective

To determine the spawning seasonality of two highly targeted jacks (Carangidae; Giant Trevally [known in Hawai’i as ulua aukea] Caranx ignobilis and Bluefin Trevally [known in Hawai’i as ‘ōmilu] Caranx melampygus) within Hawai’i through a collaborative effort with local fishers.

Methods

By working with volunteer fishers, we collected gonad samples for Giant and Bluefin trevally throughout a 15-month period on four of the main Hawaiian Islands. Spawning seasonality was assessed using histological gonad samples as well as mean monthly gonadosomatic index (GSI).

Result

Fishery involvement proved successful in collecting biological samples needed to understand the spawning seasonality of these species. Participants were able to macroscopically identify when females were spawning versus undeveloped following initial instruction from the researchers. Mature female GSI resulted in similar conclusions as histological analyses. Both species had a spawning season between February and September, with peak spawning occurring from May to July. During the spawning months, a semilunar spawning pattern was observed for Giant Trevally with peak GSI occurring shortly before the full moon. Bluefin Trevally had higher variability, with no distinct lunar periodicity.

Conclusion

Training fishers to be a part of the scientific process and collect gonad samples created trust in science and interest in learning more about the biology of their catch. By consistently sharing our progress and results through social media we were able to engage and build trust with the greater fishing community.