Sundarbans fisheries: a model system for the application of landscape ecology and social science approaches to management

Coastal ecosystems provide important services to human communities, the most well-known being food provision from fishing. Fisheries are critically important, providing food security and income to communities worldwide. However, the removal of marine species and damage to marine habitats from fishing activity may affect other services, like coastal protection and carbon capture. Other industries that depend on healthy marine ecosystems and biodiversity, such as tourism, may also be affected. Fishing activity can also damage resources on which targeted fish species depend, including important nursery areas for young fish.

In response to declines in fish numbers and environmental damage many countries have signed international agreements to use an "ecosystem approach" to fisheries. An ecosystem approach links fish and their environment. To do this we need to understand what aspects of the marine environment are important to fish. A typical method has been to identify "essential fish habitat" - the type of seabed which seems to be most important to the fish in question. This method identifies one essential fish habitat and differs from best practice on land, where we have long recognised that species use different habitats through their lives. On land, we understand that different habitats need to be linked so that animals can move between them. This "landscape ecology" approach is not applied to fisheries management, as we lack sufficient information about spatial distribution of different seabed types and biodiversity patterns across underwater landscapes.

Using underwater camera systems and seabed maps we have previously demonstrated that fish in a UK marine protected area are affected by the seabed type and biodiversity in their immediate area, and also by the wider landscape. Using underwater landscape information has huge potential to improve management of fisheries in the developed and developing world. But we need sufficient information about the different habitat types, biodiversity patterns and how fish are affected by them.

This presents a paradox. How can we test and develop ideas of huge scientific and practical value about fish landscape ecology without incurring the great expense associated with biodiversity and environmental mapping? How can we persuade others to pay for the necessary mapping without more evidence of the usefulness of marine landscape approaches?

Fortunately, a suitable landscape exists in the Sundarbans Mangrove forest (SMF). The project partner, Sarker, has carried out a mapping and modelling project which has resulted in a comprehensive map of the physical and biological characteristics of the SMF. The waters in this forest are rich fishing grounds, providing food and livelihoods to millions. However, fisheries in the SMF are in trouble and lack any effective management.

We will sample fish throughout the SMF to understand what aspects of the SMF environment are associated with increased abundance, diversity and size of fish. We will investigate how fish are affected by their immediate environment and also how they are affected by the landscape around them (whether it is a patchwork of different habitats, or a uniform environment consisting of one habitat type).

We will also interview fishers to understand how they choose where to fish, and whether they use the same types of signs that we detect from our sampling. In particular, we want to know whether fishers consider the wider landscape around their fishing locations, or just the immediate environment. These questions are important as we need to know how to choose management measures which do not hinder fishers, while ensuring that fish and their essential habitat is protected.

This short project will greatly develop fish landscape ecology, applicable to fisheries worldwide. The work will inform the management of the SMF fisheries so that they can provide sustainable food supplies and livelihoods.

The main economic and social impacts of this work will be in the fields of fisheries and coastal ecosystem management. The main beneficiaries will be fishers, fisheries managers and the wider society as consumers of "cultural services" provided by coastal marine environments.

Marine resource management requires the rational and evidence-based division of space in the marine environment between users, and restrictions on some activities. Scientific evidence about which areas of the coastal marine environment can be used for extractive industries and which should be protected maximises the effectiveness of protection and minimises undue interference with the sustainable use of the coastal zone. Because the evidence base for most marine protected area implementation is poor (as we have reported on the Scottish MPA process1) they often fail to achieve their conservation objectives and/or interfere unduly with sustainable use.

Our proposed approach using landscape ecology principles will be a huge future benefit to the rational management of fishing and other extractive uses of the marine environment.

Short term: Over the first year of the project our work will be used as evidence by the Bangladesh Forestry Department (BFD) to support their management of the SMF. The Management Plan Division (MPD) is particularly concerned about overharvesting and changes in salinity. Our work will help identify priority areas for protection, and help predict how ongoing salinisation will affect fisheries yields in the future. This will lead to more effective spatial management of fisheries for both biodiversity conservation and to ensure fishers can sustainably use the SMF resources. Future work as described in the "Potential for Long-term Partnership" section will further develop this potential impact.

Medium to Long term: As part of our ongoing work with the Scottish Government we are exploring landscape approaches in UK waters. The proposed study here will help develop tools and statistical approaches which will be applied to fish distribution studies in the UK. This will support the development of inshore fisheries management in this temperate zone. We would expect the impacts of this work to occur within 3-5 years. Over the next 10 years we expect landscape approaches to fisheries management and biodiversity protection to grow enormously in significance. We expect the work we will do in the proposed work to make a very important contribution to this movement.

1. Hopkins, C. R., Bailey, D. M. & Potts, T. Scotland's Marine Protected Area network: Reviewing progress towards achieving commitments for marine conservation. Mar. Policy 71, 44-53 (2016).