"INSHORE" vs "OFFSHORE" - What's the Difference?
Well, “the difference” is obviously how far the waters are from land. And the
difference appears to be fairly significant these days, especially if you are a hungry
marine animal. “Offshore” is now a much harder place to find something to eat.
The numerous declining fish stocks show a very clear trend: the farther offshore
they are, the worse trouble they are in. It is a pattern that I looked for at the outset,
realizing that more
are naturally available closer to the shorelines. There is a
whole assortment of lifeforms that live in the intertidal zone, and “runoff” from the land
containing organic nutrients occurs naturally and as the result of human activity. This
includes such things as agricultural runoff, human sewage and dissolved nutrients flushed
out of the forests, for example, by rainfall. So I looked for, and found, a pattern of fish
stocks that are disappearing more quickly from areas that are located farther away from
land. Because of the availability of terrestrial source nutrients, life in inshore waters is
not as heavily dependent on “primary production” as is life farther from shore.
Many examples can be used to illustrate the “better inshore/worse offshore”
pattern, but one good one is the northern cod in Atlantic Canada. The farthest offshore
stock (Grand Banks) is in a severe decline and shows no sign of recovery despite 8 years
relief from fishing pressure. “Inshore” Newfoundland cod, however, rebounded
somewhat after a shorter moratorium...although they are not strong enough to tolerate
even a modest fishery. Similarly in the northern Gulf of St. Lawrence cod are showing a
few encouraging signs. Their key to success and the reason they are growing better than
their cousins on the Grand Banks is their location. They are near the mouth of the St.
Lawrence River which carries a load of nutrients from central Canada, also they are in
close proximity to the shoreline of Quebec, so the productivity of the intertidal zone
would contribute. Farther from the mouth of the river however, in the southern gulf, cod
are doing very poorly. The same pattern is evident in many other places as well,
including the groundfisheries on the west coast of Canada and off Southwest Nova
Scotia, where the “fishing effort” has been continually moving closer to the mouth of the
Bay of Fundy. It is also very clearly illustrated in the growth of scallops in the many
different “scallop fishing areas” inside and outside the Bay of Fundy and surrounding
area. This pattern is consistent with a “starving” ocean that is increasingly dependent on
whatever nutrients are returned from the land.
Going far offshore and dragging up every fish that we can find, and then just
“giving back” a bit of sewage around the edges...seems to me like a rather negligent way
of looking after an ocean ecosystem.
I received a recent comment to the effect that:
“How is it that if the ocean is starving, it seems to support such large populations
of top predators, i.e. marine mammals...in California sea lions appear to be above historic
numbers...how can this be? Ditto for northern elephant seals...Both these species are
increasingly occupying mainland habitat, including un-natural habitats like docks and
breakwaters. If food is a limiting factor, this threshold appears to not have been reached
yet. In addition, several whale species appear to be increasing annually in our local
waters, including blue whales, fin and humpback. If the ocean is starving, how does it
support increasing populations of marine mammals?”
A expert on whales countered the impression that populations of these animals
are on the increase, that is apparently not proven. Marine mammals like whales however,
are increasingly being seen in waters closer to shore (this has been noted along the
Atlantic coast as well). Knowing that fish are becoming very scarce offshore compared to
inshore, it becomes obvious why sea lions and elephant seals are “increasingly occupying
mainland habitat.” Unfortunately this tendency of whales to forage in inshore waters now
probably also places them at greater risk of entanglement in fishing gear, which has also been set
inshore...because that’s where the last fish are.
The pattern of a steeper decline in offshore fish stocks as compared to inshore
ones is not particularly subtle. It’s definitely there. And I think it is one more trend that
casts doubt on the “climate variation” explanation for the declines in marine animal
“Climate” varies over time, not as you travel farther from the shoreline...