Sea. Some years, Nomura’s jellyfish are most prominent along the Korean coast,
some years along the Japanese coast. Reaching Tsugaru Strait, the coastal flow carries
them into the Pacific and south along-shore of Honshu. In many recent years they
have been sufficiently numerous to stop all trawling. Netting just one or two fully
developed medusae creates a serious problem for fishing machinery. The economic
impact on Japanese and Korean coastal fisheries is substantial. Richardson et al.
(2009) provide a general review of the many jellyfish “problems” worldwide.
(^) Fishing quite consistently interacts with climate variations to become over-fishing.
We leave this topic to other authors. For a clean statement of how management and
politics interact to prevent limitation of fishing to sustainable levels (in so far as the
habitat is consistent enough for any semblance of sustainability) see Rosenberg
(2003). For a review of the depletion and failure to recover of the northwest Atlantic
cod fisheries, see Rose (2004).
(^) The technology of some fisheries is relatively benign, apart from the fish killed.
Hauling a trawl or trolling baited hooks through mid-water probably does not damage
the biota significantly, apart from the fish targeted and captured. But hauling trawls
right against the bottom is another matter entirely. The “tickler chains” of large
benthic trawls are hauled though the upper layers of sediment, capturing or breaking
masses of invertebrates, plowing the sediment to several decimeters depth, leaving in
some habitats a wasteland that takes years to regenerate (e.g. see Jennings et al.
2001). Some heavily trawled bottoms, such as Georges Bank or the eastern English
Channel, probably have not approached anything like a natural, untrawled condition
in many decades. In fact, into the early 19th century the seabed of the North Sea was
entirely covered with oyster beds (Roberts 2007). Early trawlers pulled heavy chains
over the whole region to improve the habitat for plaice and sole, and now it is all mud
and sand. That is good if you like plaice and sole. In some cases, nearly natural
benthic habitat conditions may be required for maintenance of the fish stocks that are
targeted by the trawlers that disrupt the bottom. Thus, fishing not only removes fish,
but also can hamper stock recovery. The entire issue has come strongly into public
attention since the late 1990s, and work is under way to evaluate and mitigate trawl
damage. Les Watling, a benthic ecologist, has been a leader on this issue (Watling
2005).
(^) Lost gear of all kinds becomes part of the marine environment for a long time. Crab
and lobster traps that have lost their surface floats continue to collect. Latching escape
doors with corrodible clasps that last only a little while beyond the anticipated pull
date can alleviate this. Synthetic fibers now used almost exclusively in trawls and gill
(drift) nets last many years adrift in the ocean. Every mariner has seen seals and
whales struggling to swim while stuck in a blanket of old mesh, suffering a slow,
tortured death. Lost gill nets go on fishing and fishing, sometimes for years,
entangling both fish and mammals. Mammals, particularly the harbor porpoise in