"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 nutrients 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 populations. “Climate” varies over time, not as you travel farther from the shoreline...