1.1 - Bycatch - a short definition
"Imagine the meat in your supermarkets would be obtained by mass bombing the forests of the world and collecting whatever we find and need while simply discarding the rest and leaving behind nothing but burnt soil. This is more or less what we do to the sea.[i]"
(Master Makani in "Orcaworld")
According to the Lighthouse Foundation - a German not-for profit Marine advocacy organisation established by the City of Hamburg - more than 27 million tons of fish and other marine organisms are caught as bycatch and discarded each year. The numbers differ from source to source, but all in all roughly one third of the entire catch is bycatch and ultimately ends up as "discard", in other words: the caught animals are thrown over board and in most cases don't survive. Life animals are simply dumped for no particular reason. In part bycatch is the result of inappropriate and highly unselective fishing methods and equipment leading to indiscriminating fishing. The fishing areas also play a role as the makeup and behaviour of marine populations differ from region to region.
Bycatch of Shrimp Fishing (Source: NOAA)
A less common definition of bycatch is the discard of sharks resulting from the practice of shark-finning, where the shark is, so to say, bycatch to itself. Estimates sharks killed in this process range from 26 million to 78 Million annually[iii]. Bycatch drastically aggravates the global overfishing situation and contributes to species decline, ecosystem shifts and environmental change on all levels.
1.2.1 A complicated Issue
The problem has causes, reasons and implications on and in many interlocked levels and arenas, ranging from practical and technical aspects of fishing methods and methodologies over sociological, economical and philosophical/ethical topics all the way to the murky waters of international politics. The following are some fishing methods connected to bycatch.
1.2.2 Technology mesh sizes and dredging
The topic that is most easily addressed is technology improvement, especially since improved fishing methods and techniques in many cases not only significantly (sometimes drastically or near completely) reduce bycatch - they also have the side effect of reducing efforts for the fishermen and hence come with economic incentives attached to them. In any case avoiding or reducing bycatch required significant skills on the side of the fishermen and demands well thought through and excellently designed equipment. The type of bycatch also is a function of, among other factors, the setting of the fishing gear and the respective sea floor composition. Necessary know how on the side of the fishermen includes fisheries biology. They must have regional knowledge of species distribution as well as preferred spawning grounds and location of young fish stocks. It is common knowledge among men of the craft that fish below a certain size - Haddock under 25 cm and Cod below 35 cm had not yet spawned, and every fisherman knows how to handle his nets and gear to catch fewer small fish - fish he now would discard and that would later be missing as part of his valuable catch. The most common method to control the catch is by varying the mesh sizes. Increasing mesh sizes reduces bycatch of smaller fish while decreasing it increases it, up to the level where practically everything in the way of the net is caught, which is, for example, the reason for the enormous amounts of bycatch in classical shrimp fisheries. Such fine meshed nets result in a catch of up to 90% undesired species, derogatively called "trash fish", which generally is thrown over board due to its low economic value in comparison to shrimp.
The main method applied in shrimp fisheries and bottom ìharvestî of sea food - such as shells and bottom dwelling fish - is dredging. Dredging not only catches practically everything alive in, on or near the sea floor, it also strongly impacts the habitat itself by literally ploughing the surface. The true impact of this practice on benthic communities and beyond is difficult to assess, since the knowledge about marine habitat variability is scarce. However, in a long term experimental study of scallop fisheries comparing dredged to non-dredged sea floors in Port Phillip Bay, Australia, [Currie and Parry ,1996] have found that even 14 months after the last dredging event occurred, some benthic species had not yet recovered. The result is a change in community structure of the benthos. The same research also indicated that changes by community structure were below the natural seasonal and weather event induced variation[iv]. At first site this appears to be an encouraging result, but since the overall sensitivity of benthic ecosystem over longer periods of time is poorly understood it is difficult to assess such results in terms of an environmental impact statement. Small impacts significantly below natural variation can still be a strong enough signal in a dynamic system to result in significant changes all the way to collapse. It is common knowledge in ecology that diversity is a prerequisite for durability and nature can be significantly more tolerant to change than expected. It also is equally common sense that change and adaptation have always been a part of the natural environment.
A particularly irresponsible form of fishing is by means of drift-nets, which hover in the sea as invisible and for many marine species practically undetectable curtains only moved by wind and currents. These "curtains of death" indiscriminately catch everything crossing their path, be it turtles, marine mammals like seals, sea lions, whales and dolphins or sharks, sea birds and many other victimized non-target species ending up as unwanted bycatch. Despite a ban of drift-nets exceeding 2.5 km in length there still are nets of lengths with up to 50 Kilometres continuously drifting in the oceans of seas of the world. But not only net types like drift nets or gill nets are an enormous threat because of their tendency to produce large amounts of bycatch. Another significant problem is long-line fishery, applying lines with lengths of several kilometres and equipped with thousands of hooks with lures. Although this in general is a highly selective catching method, many other animals go after the lures and therefore are caught, including sea turtles, sharks, marine mammals and marine birds - especially Albatross. In fact Albatross are now altogether endangered by long-line fisheries. Other disastrous fishing methods are purse seining and drag-netting. Purse seining in the tuna fisheries was the one fishing method that brought the whole bycatch and discard problem to public attention, mainly because the method included targeting dolphins, which were used as an "indicator species" since they often hunt together with tuna.
1.2.4 Ghost Fishing