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- Objectives
- Broadly describe the trophic ecology of skipjack tuna in the EPO using classical stomach-contents analysis
- Quantitatively disentangle spatial, temporal, and ontogenetic differences in diet to identify important habitats of skipjack and their forage
- Background
- Early accounts of skipjack stomach contents in the EPO have been limited to measurements of prey volume by size class with sampling strata determined a priori based on presumed areas of high skipjack densities
- Other studies have used calculations of prey weight, number and frequency of occurrence of skipjack sampled opportunistically throughout the EPO
- Little attention has been placed on quantitatively assessing the potential relationships between oceanography, ontogeny and skipjack feeding ecology Such information is essential for informing a planned spatially-explicit ecosystem model of the EPO (Project O.2.b) to account for direct and indirect impacts from fishing on the ecosystem, as mandated by the Antigua Convention
- Relevance for management
- Quantifying trophic linkages in ecosystem models provide descriptions of the magnitude of biomass transfer through the ecosystem and assist in assigning a more reliable proportion of both predator and prey in spatial strata using spatially-explicit ecosystem models, such as Ecospace.
- Duration
- 12 months
- Workplan and status
- Task 1: Exploratory analysis of skipjack tuna diet data
- 1.1: Map locations of skipjack stomach samples overlaid with Longhurst biogeochemical Provinces;
- 1.2: Assess size distribution of skipjack sampled for stomach-contents analysis;
- 1.3: Explore the relationship of predator-prey size.
- 2.1: Compute gravimetric, numeric and occurrence indices of diet composition to examine prey importance;
- 2.2: Run classification trees using skipjack diet data as the response variable and Longhurst Province and skipjack size as the explanatory variables;
- 2.3: Interpret results with respect to ecosystem-related goals outlined in the SSP;
- 2.4: Prepare manuscript
- External collaborators
- CICIMAR, La Paz, Mexico
- Deliverables
- Manuscript that contributes to IATTC’s ecosystem approach to fisheries management through identification of ontogenetic functional groups and quantifying their predator-prey interactions for use in ecosystem models.
- Updated date: 01 May 2021
- Progress summary for the reporting period
- A manuscript entitled “Spatial and ontogenetic relationships in the trophic ecology of skipjack tuna, Katsuwonus pelamis, in the eastern Pacific Ocean” was submitted for publication in the journal “Marine Biology” in December 2019.
- Challenges and key lessons learnt
- An extensive exploratory analysis is essential for appropriate interpretation of the classification tree results. Sampling multiple fish from the same purse-seine set can influence the results highlighting the importance of designing a statistically robust sampling protocol.
- A manuscript entitled “Spatial and ontogenetic relationships in the trophic ecology of skipjack tuna, Katsuwonus pelamis, in the eastern Pacific Ocean” has been submitted for publication in the journal “Marine Biology"
- Comments
- This project will help improve diet matrices in EPO ecosystem models.