MODELLING THE TROPHIC ROLE OF MARINE MAMMALS IN TROPICAL AREAS: 

DATA REQUIREMENTS, UNCERTAINTY, AND VALIDATION

Fisheries Centre Research Reports 17(2) 2009

By:  Lyne Morissette, Jenny Lynn Melgo, Kristin Kaschner and Leah Gerber

Download this report: Full Report

ABSTRACT

This Fisheries Centre Research Report includes two papers that describe whole-ecosystem models of two tropical breeding areas for baleen whales: Northwest Africa and the Caribbean. A mass-balance model, sources of data, and derivations of model parameters are detailed for each region. Exploration of the different sources of uncertainty and their effects on the modelling outcomes are also provided. Analyses based on these models examine the potential competition between whales and fisheries for marine resources.

DIRECTOR’S FOREWORD

This document demonstrates the importance of making the best use of local data while addressing critical issues in marine ecology and fisheries management. So far only few attempts have been made to describe the foodwebs in data-scarce areas of the world such as Northwest Africa or the
Caribbean. However, whenever such attempts have been made, one realizes that hidden treasures do exist in such cases. Moreover, when data is integrated into a foodweb model, we gain a lot of knowledge by examining that whole ecosystem and determining where more data and research are needed, which can be very fulfilling.

Indeed, once we have a complete description of the whole food web, not only can we learn about the dynamics of the system and the ecology of each species included in it, but we can also discover indirect effects that the complexity of these systems holds. These indirect effects are only seen when examining the whole ecosystem structure, and can lead to counter-intuitive impacts on some trophic groups by others. In the case of marine mammals and their interaction with fish and fisheries, these effects can become very important conservation matters.

Marine mammals are part of ecosystem complexity, and often, they are not considered in models built for fisheries management. By applying an Ecopath with Ecosim approach, this report demonstrates that these animals can be incorporated in marine ecosystem models, and that their role in structuring the ecosystem is important. Thus, assessing their impact on the ecosystem or their interactions with fisheries requires a holistic overview of the ecosystem complexity, not only an assessment of predator-prey issues involving two or three species.

The ‘whales eat fish’ issue is a major point of discussion internationally, and more importantly in tropical countries who are highly depending on marine resources and where fisheries have encountered severe declines over the last decades. When addressing a very socio-politically complex issue such as the interactions between marine mammals and fisheries, it is crucial to make the best use of the data available in tropical countries and to integrate that into an ecosystem approach. A key contribution of this report is that it represents the most updated database on the biology and ecology of all marine organisms in two tropical ecosystems: the Caribbean and Northwest Africa. This was not only collected through an in-depth literature review, but also validated by many local experts in both areas during workshops held in Bridgetown, Barbados, and Dakar, Senegal.

Once again, the current report demonstrates how one of the key areas of research at our Centre can be used to provide insights into fisheries that would otherwise not be studied at the ecosystem level because of the usual excuse of “no data”.

RASHID SUMAILA, DIRECTOR

UBC FISHERIES CENTRE