Fishery Interactions/Entanglement
Marine
mammals in the U.S. Northwest Atlantic interact with a wide range of
fisheries and fishing gear, although data on the level of interaction
or is incomplete for most fisheries. The regulation of commercial fishery
interactions with marine mammals is controlled mainly by the Marine
Mammal Protection Act (MMPA). Section 118 of the Act categorizes each
fishery according to its level of interaction or "take" with
marine mammal stocks. Category I fisheries are those where takes are
frequent, while Category II fisheries are those with occasional takes.
Under this classification system, one take equals one mortality, although
this system is subject to change under the 1994 amendments to the MMPA.
According
to the NMFS, there were four Category I and four Category II fisheries
operating in Northeast waters during 1992-1993 (Marine Mammal Exemption
Program - List of Fisheries). Category I fisheries include the Gulf
of Maine small pelagic surface gillnet, New England multispecies sink
gillnet, Atlantic swordfish, tuna and shark gillnet and Mid-Atlantic
foreign mackerel trawl fishery. Category II fisheries included the Mid-Atlantic
coastal gillnet, Atlantic swordfish, tuna, shark longline, Atlantic
swordfish, tuna, shark pair trawl, and Mid-Atlantic mackerel trawl.
The species most frequently affected by these fisheries include: harbor
porpoise, common dolphin, harbor and grey seals, Atlantic white-sided
dolphin, pilot whales, bottlenose dolphin, Risso's dolphin, minke, humpback,
and northern right whales.
The extent
of interaction between marine mammal and commercial fisheries in the
waters of Massachusetts Bay and Cape Cod Bay (including the Sanctuary)
is known largely through the reporting of takes by aboard observers,
logbook entries submitted by fishermen, disentanglement efforts by the
Center for Coastal Studies, sightings of animals trailing gear, scars
attributed to entanglement, and strandings. Despite these sources, the
severity of the impact of these interactions on discrete populations
is difficult to quantify. However, in general reported mortality rates
are near 100% for the phocoenids (porpoises) and delphinids (dolphins),
and appear to decrease with increasing size of the animal (Kraus, 1990a).
According
to Kraus (1990a) there were 428 documented marine mammal entanglements
from 1975-1989 in the Gulf of Maine (GOM) and the New York Bight. These
entanglements involved ten species of cetaceans and two species of pinnipeds,
with gillnets responsible for more than 66 percent of all entanglements.
Harbor porpoise accounted for most (87%) of the documented takes in
gillnets.
Entrapment
and entanglement in active fishing gear is the most frequently identified
source of human-caused injury or mortality to humpback whales (NMFS,
1991a). Between 1976-1986, 18 humpback whales were reported entangled
in fishing gear in northeastern U.S. continental shelf waters. Of these,
nine were freed by rescuers, 6 died, and 3 escaped with some gear still
attached (ibid.). Approximately 40 percent of the humpback whales in
the GOM file population exhibit scarring attributed to fishing gear
(Carlson, pers. com.).
For northern
right whales, twelve encounters with fishing gear were recorded in the
western North Atlantic between 1975 - 1991 (NMFS, 1991b). Four of these
occurred within Massachusetts Bay. Analysis of New England Aquarium's
photographic catalog of right whales show that 58 percent of the catalogued
animals have scars or injuries indicative of rope and net cuts (ibid.).
With
regard to those populations which frequent the Sanctuary, harbor porpoise
is the only species where an attempt has been made to determine the
biological significance of incidental take at the population level (Smith,
et al. 1993). In this instance, data obtained from the NMFS observer
coverage and fish landings (weighout) were used to estimate the total
bycatch rate of harbor porpoise in the New England multispecies sink
gillnet fishery. This fishery, which operates throughout the GOM from
Cape Cod Bay to Eastport, Maine, occurs primarily inshore (within 100
fathoms) with areas of concentrated fishing effort (and takes) shifting
seasonally according to target species abundance. Estimates of bycatch
decreased slightly from 1990 -1993, from 0.05 - 0.03 percent of the
estimated abundance, but the bycatch rate for Gulf of Maine alone remains
above the recommended allowable take rate of 0.02 used to manage small
cetacean species (Palka, 1994, Bisack, 1993, Read, et al., 1993). Although
many uncertainties remain regarding population structure and growth
rates for this species, as well as the magnitude of bycatch from fisheries
impacting the population outside the GOM, efforts to reduce the bycatch
rate have been adopted.
In April
of 1994, the New England Fisheries Management Council instituted a Framework
Adjustment to its NE Multispecies Fishery Management Plan which established
seasonal time and area closures directed at the sink gillnet fishery.
Accordingly, some of the western and southern portions of the Sanctuary
are incorporated in the March 1-30 Massachusetts Bay closure. Two other
much larger time and area closures were developed for the mid-coast
and northeast area of the GOM. In addition, the Massachusetts Division
of Maine Fisheries is considering a March gillnet closure for all of
Cape Cod Bay in an effort to bolster protection provided under the federal
closure and to further protect the northern right whale from the threat
of entanglement due to the potential for effort displacement into the
Cape Cod Bay right whale critical habitat (Jim Fair, pers. com.).
As a
final note, estimates of entanglements from outside of U.S. territorial
waters, particularly from the Atlantic Canadian provinces may impact
the seasonal populations which occur within the Sanctuary. As mentioned
above, the Gulf of Maine/Bay of Fundy population of harbor porpoise
are known to be subjected to rather high levels of mortality from Canadian
fishery interactions, although no firm estimates are available. Lien
(unpub. data, 1991) reported approximately 135 humpback whale entrapments
in fishing gear for Newfoundland. Fortunately, with Dr. Lien's assistance,
many of the humpbacks trapped in Canadian weirs are able to be released
alive.
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