Competition for Available Resources
Competition
for food resources in the marine environment involves many direct and
indirect interactions between predator and prey species. For example,
seals typically feed upon many different kinds of fish and as one species
becomes scarce, they may switch to other more abundant species, thus
allowing recovery time for depleted stocks. Fishing activities may interrupt
this cycle by prolonging, or in some cases preventing, recovery of overexploited
stocks (Bonner, 1990). Fishing pressures may also stress predator-prey
relationships in ways which influence marine mammal distribution and
abundance (Payne, et al. 1990).
Alternatively,
marine mammals may compete both directly and indirectly with man for
certain species of fish. Winn, et al. (1987) estimated that the total
annual food requirement for all cetaceans on Georges Bank ranges from
45, 914 mT to 460, 000 mT or an amount roughly comparable to the take
by commercial fisheries during the same time period. The authors conclude
that the role of marine mammals may be greater than previously recognized
in terms of both direct and indirect competition with man for the food
resources of the Bank. This observation is particularly significant
for northern right whales which may be in competition with planktivorous
fish for copepods (Payne, et. al., 1990).
Unfortunately,
direct comparisons between the role of cetaceans on Stellwagen Bank
and Georges Bank are not possible due to a lack of information on the
food requirements and total cetacean biomass from Stellwagen, however
given the similarities in species occurrence and their preferred prey,
it is likely that cetaceans consume a significant amount of the fish
productivity in the sanctuary area as well.
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