Skipjack Tuna Availability for Purse Seine Fisheries Is Driven by Suitable Feeding Habitat Dynamics in the Atlantic and Indian Oceans

Abstract

An Ecological Niche model was developed for skipjack tuna (Katsuwonus pelamis, SKJ) in the Eastern Central Atlantic Ocean (AO) and Western Indian Ocean (IO) using an extensive set of presence data collected by the European purse seine fleet (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014).Chlorophyll-a fronts were used as proxy for food availability while mixed layer depth, sea surface temperature, dissolved oxygen, salinity, current intensity, and height anomaly variables were selected to describe SKJ's abiotic environmental preferences. The resultant ecological niche included both mesoscale eddy-type productive features that displayed latitudinal range in the IO to large scale upwelling systems that shrink and swell seasonally in the AO. Overall, 83% of all free swimming school sets (FSC) and 75% of drifting fish aggregating device sets (dFAD) that contained SKJ occurred within 25 km of favorable feeding habitat. In the AO, 34% of dFAD sets were made more than 100 km away from this habitat, mostly in the surface chlorophyll-a poor environment of the Guinea Current. These distant sets represent 10% of dFAD sets in the IO and 8% of all FSC sets. Our results suggest that the Mozambique Channel in the IO, with its simultaneously favorable feeding and spawning conditions, may seasonally offer a better SKJ nursery habitat than the Guinea Current which shows a substantially poorer feeding capacity. With the exception of this latter area, our results also suggest that fishing accessibility will be higher in months where the size of the favorable feeding habitats are reduced, likely because this reduction drives a geographical contraction in SKJ populations. The observed relationship between the annual size of favorable feeding habitat and both annual catch rates and total catches in the IO is consistent with the near-full exploitation of this stock that has occurred since the 2000s. Moreover, it suggests that annual habitat size could be used as an indicator of growth capacity for this highly productive stock. Habitat monitoring, as part of a dynamic fisheries management approach, should contribute to the sustainable exploitation of SKJ by providing information on the climate-dependent aspects of stock variability and the effects of dFAD deployment in food-rich habitats.

Seasonal variability in global industrial fishing effort

“…For example, cephalopods, with very fast life cycles, respond particularly strongly to seasonal variations of production [39]. The second potential source of variability in B , fish movement, can occur through seasonal migrations for reproduction [40] or seasonal contraction of habitat [2, 17], both of which can drive a change from widely dispersed to concentrated. Thus, fish movement can drive local seasonal increases of B for the same overall population size.…”

“…The seasonal interactions between the environment and fishers is often locally well known at the level of stocks [6–8] or for ecosystems [9, 10], for both industrial [11, 12] and small-scale fisheries [13, 14]. Models have been developed in order to analyse how natural and socio-economic drivers shape the seasonal dynamics of fishing effort, for single- [15–17] and multi-species fisheries [18]. In addition, tools that forecast the seasonal dynamic of marine resources are now being implemented to assist management [19].…”

The key role of the Northern Mozambique Channel for Indian Ocean tropical tuna fisheries

“…Skipjack larvae predominated in the NMC and tuna larvae were the most abundant during November-April (Conand and Richards 1982;Beckley and Leis 2000). Although the Mozambique Channel appears to be a relatively poor feeding habitat compared to other areas of the western Indian Ocean such as the Somali basin (Druon et al 2017), the warm waters (>27°C) of the area combined with mesoscale activity that enhances enrichment through mixing and retention (Tew Kai and Marsac 2010) may constitute optimal environmental conditions for tuna spawning (Reglero et al 2014). New reproductive studies specifically focusing on samples collected throughout the year within the NMC combined with ichthyoplankton surveys would be essential to fully resolve the role of the area for tuna spawning and stocks recruitment.…”

Large‐scale distribution of tuna species in a warming ocean

“…() described the global habitat preferences of commercially valuable tuna, but did not explore historical or future changes in these distributions. Other regional, single ocean, or single species efforts have projected tuna distribution and tuna population responses to climate change (Bell, Reid, et al., ; Christian & Holmes, ; Druon, Chassot, Murua, & Lopez, ; Dueri, Bopp, & Maury, ; Lehodey, Senina, Calmettes, Hampton, & Nicol, ; Michael, Wilcox, Tuck, Hobday, & Strutton, ). For example, studies on Pacific Ocean skipjack project significant changes in their abundance and spatial distribution (reduction in most tropical waters and expansion in higher latitudes) in the future (Dueri et al., , ; Lehodey et al., ).…”