By Simon Northridge of the School of Biology at the University of St Andrews, Scotland and member of ICES working groups on Bycatch of Protected Species (WGBYC) and Marine Mammal Ecology (WGMME)
Unintended mortalities
We all know you can't make an omelette without breaking eggs, and so it is with most forms of food production: there is always some breakage or 'collateral damage'. In terrestrial systems this usually involves the substantial modification of the environment through farming, massive loss of biodiversity on farmland, and control of 'undesirable' or pest species.
Fishing, although arguably less destructive than farming, also impacts the environment in unintended ways. There are very few methods of harvesting marine life that don't affect non-target species in some way. This is an uncomfortable truth, but one we have to deal with in a world whose population is over seven billion and growing, and where 16% of the animal protein consumed globally comes from wild fish.
The unintended destruction of marine life as a consequence of fishing is often expressed in terms of waste: a waste of resources, potential or life. There is another more insidious concern as well, that pressure from fishing may accidentally push some vulnerable species towards extinction, or at the very least significantly impact their numbers or distribution. Examples are not hard to find, especially amongst the more iconic long-lived species that are particularly vulnerable to incidental capture during fishing operations. We usually refer to this as bycatch – the incidental capture of individuals that were not intended to be caught.
The effects of bycatch
The recent extinction of the Yangtze River dolphin was brought about in large part through bycatch: frequent entanglement in longlines was one of the primary drivers of the species' extinction. The enigmatic vaquita (or the Gulf of California harbour porpoise), one of the smallest of all marine mammals, is now mainly confined to the Colorado River delta in the upper Gulf of California in Mexico. Numbers have been estimated at irregular intervals and the total population has dwindled from a few hundred in the 1980s to an alarming few tens of individuals at present. The species is known to be particularly vulnerable to bycatch in legal and illegal gillnet fisheries, and this is the main threat to their existence; it seems likely that the species could also soon be extinct as a consequence of bycatch.
It is not just literal extinction that is worrying. Bycatch can also lead to the commercial extinction of fish species (the species becomes so rare it is not possible to target it profitably), or to a species becoming absent from a part of its range due to extreme levels of bycatch. In European waters, fishes likes sturgeons and common skates have been affected in these ways, while harbour porpoises have been reduced to extremely low densities in parts of their European range, almost certainly as a result of bycatch.
The ecosystem approach
The ecosystem approach to fisheries management, championed by ICES and many other agencies, obliges us to consider the effects of bycatch on vulnerable species. Mammals, birds, turtles, and slow-growing fish species are all potentially vulnerable to the effects of bycatch. ICES has recently tried to get to grips with this issue through the work of a number of working groups.
First off, we need to understand the scale of any impact by quantifying the frequency with which vulnerable species might become caught. This will vary depending on the fishing gear being used, the fishery area, and season. Beyond that, we need to know enough about the abundance and population dynamics of all the species concerned to identify those for which bycatch levels may be too high. Finally, where bycatch levels are deemed to be too high, we need to find management measures that will reduce bycatch rates of vulnerable species.
Monitoring fisheries
Increasingly both consumers and retailers demand to know where their food has come from and how it has been harvested and to understand the impacts that harvesting may have had on the environment. There is therefore a need to document fisheries and detail the nature and level of bycatch.
ICES Working Group on Bycatch of Protected Species (WGBYC) co-ordinates and collates these sorts of data from across the EU, and in the wider Atlantic. One important source of information comes from the implementation of European Council Regulation 812/2004 on cetacean bycatch, which requires EU member states to monitor certain key fisheries for cetacean bycatch. Over the past ten years, these monitoring data have been submitted annually to the European Commission and to ICES. Additionally, on-board fish discard sampling schemes can, in some cases, also provide measures of bycatch rates of vulnerable species.
Some member states, recognizing the need to understand the wider impacts of fishing, have used their dedicated cetacean bycatch monitoring schemes to monitor all protected species bycatch. Slowly, WGBYC is building up a picture of both the susceptibility and the vulnerability of Protected, Endangered or Threatened Species (PETS) to fishing activity in many different fisheries throughout the EU.
One key issue under discussion is how EU member states should distribute sampling of fishing activities (by nation, area, gear type) in order to best inform the necessary risk assessment in a climate of financial restriction. We will need to improve, rationalize, and harmonize sampling to understand where the main risks to PET species at the population level are most likely to exist.
Defining reference levels
Quantifying bycatch is not the only aim; reference levels – the minimum level of bycatch that might represent a conservation threat – are also needed to alert managers if and when management actions are required. Typically this involves figuring out a reference level. If this is exceeded, some management action is flagged.
Of course what is needed above all is a clear indication of what a 'conservation threat' looks like. Reference levels, and indeed officially recognized conservation targets, for most species other than cetaceans are lacking.
Indeed there is considerable uncertainty about the current conservation status or population size of many PET species. This all makes bycatch assessment a challenging task. In many situations, a risk based approach may be advisable.
A risk based approach to understanding PET species bycatch may aim to highlight likely problem species and areas, but it can also be used to pinpoint specific fisheries or areas where more sampling would be most effective in reducing uncertainty. Vulnerable bycatch species are usually caught in more than one fishery and in more than one area, so it makes sense to focus on areas or fisheries that are most likely to contribute most to any conservation threat, and this is true when deciding where to focus monitoring or where to propose management action.
Managing the risk
Management actions to limit bycatch are rarely simple to agree on. PET species are usually taken in more than one fishery, so management advice needs to consider the effects of imposing changes on several fleets. Deciding on fishing restrictions means assessing the PET species bycatch rates in the fisheries concerned, the conservation impact, and also considering the economic or social consequences.
Restrictions in one fishery may lead to increased effort in others, so the multispecies consequences of changes in fishing effort amongst gears should also be considered to avoid conserving one species by increasing the risk to another, highlighting the importance of understanding the impacts of all gears, not just those that occasionally take a high-profile protected species.
Management actions may involve effort limitations, or area specific fishing restrictions, or technical measures, such as changes to mesh sizes, or even the introduction of specific bycatch mitigation technology. Elaborating the best way to achieve bycatch limitation targets may require expensive gear technology trials and an experimental approach to determining optimal solutions; perseverance is required.
Future uncertainty
Developments in EU fisheries management pose challenges to addressing bycatch in an ecosystem based approach. On-board fishery monitoring, whether for bycatch or other purposes, may in the future all be subsumed into a single data collection framework, with a potential risk of a loss of focus on PET species.
In the meantime, integrating bycatch concerns with stock management advice is challenging, as most stock advice to managers is given in terms of Total Allowable Catches (TACs) and quotas, regardless of the gear types involved in taking those quotas. In contrast, bycatch assessment is usually framed within a perspective that is focused on differences in gear types regardless of the target fish, which can lead to two different streams of advice. Exactly how these two advice streams can be harmonized to produce a coherent management strategy remains to be elaborated.
