American shad in the Pacific: Seth Green's finches

although we don’t see them here on the Sunshine Coast very often, occasionally, depending on the time of year, the run and the prevailing weather circumstances, we do catch the odd American Shad (Alosa sapidissima), a fish which “doesn’t belong” here or in fact in the Pacific, a fish from the Atlantic Ocean and the US- and Canadian East Coast. In the Atlantic area and East it is highly prized as a sport fish and delicacy; here on the West Coast it is largely overlooked and ignored. And yet it is by a long stretch my absolute favourite fish; not for sport or food but because it doesn’t belong here, does nevertheless so well without doing damage to other fish stocks and because of its apparent adaptability.

in 1871, American Shad, from his nursery on the Hudson River (Albany, US), was introduced by Seth Green (and another transfer by Livingston Stone in 1873, also from the Hudson River) into the Sacramento River (California, US), in an attempt to establish the highly successful and profitable shad roe fisheries from the American East Coast on the Pacific Coast. The species established itself rapidly and spread along the Pacific Coast northwards at a rate of 100-200 km per year.

as early as 1876 mature shad were spotted in the Columbia River and they were caught off the west coast of Vancouver Island. In 1885 additional fingerlings from the Susquehanna River (US, Pennsylvania), a run now almost eradicated but in the process of being re-established with stock from the Delaware and Columbia (!!) Rivers, were released in the Columbia River (Washington and Oregon), and by 1891 mature shad were taken in the Fraser River (BC) and Stikine River (Alaska). By 1926 shad were taken at Karluk, Kodiak Island and more recently in the Anadyr River (Russia, Siberia) in the north-western part of the Bering Sea. Shad have become very abundant in the Columbia River system, with as many as 4 million shad estimated as returning for spawning in 1990 and annually beyond. Ironically the story of American shad in the Atlantic and East Coast river systems is far less positive; basically significant decline and a serious struggle to try and re-establish shad in many locations.

so in very short time, a species originating from the East Coast of the US established itself in an area and environment where it had not previously occurred and which had no other shad or shad-related species. The transfer and subsequent successful permanent establishment of A.sapidissima is of interest for a number of reasons.

- first of all the Pacific Ocean, its warming currents and coastal configuration has proven to be highly supportive of shad, and yet there are very few even remotely related native species, and none of which of the Alosa family, resident in the Pacific, despite the fact that not all that long ago (on a geological timescale), the Atlantic and Pacific were connected both at he arctic and Central America which didn’t exist yet then.

- secondly, due to its geographic isolation, there is no opportunity for American shad to hybridize with other Alosids. Therefore any change of characteristics or traits within the Pacific population should be the result of natural selection within that population, and not of input from other identical or closely related species.

- finally the origins of the transplants are known with respect to their river of origin, the Hudson River in the case of the Sacramento River transplants of 1871 and 1873, and the Susquehanna River transplant of 1885 into the Columbia River. The conditions in the Sacramento and Columbia Rivers being very different from the Hudson and Susquehanna (in particular latitude but also say salinity), it can be expected that selection pressures will have resulted in differing traits over a period of 138 and 124 years (to 2009) respectively.

although in evolutionary terms one hundred or so years is insignificant (for fish of this size anyway), in terms of natural selection the timescale is such that it should be observable and we should be able to compare with the current populations from the Hudson, where “our” fish stem from, what differences there are now. In fact what we have here is potentially and totally unexpectedly a marine equivalent of the Galapagos Islands where Darwin discovered and studied differences in finches on different islands, Darwin’s finches.

but there’s more……

we know actually very little about American shad other than where and when it spawns and what it does during that time and virtually nothing about its deep-sea phase, which means the bulk of its adult life span. This is not that unusual; we have the same problem, more or less, with one of the best studied populations of marine fish in existence: Pacific salmon (and probably Atlantic too). Unsurprising as out in the ocean, like salmon, it disperses over vast distances. There are lots of interesting tit-bits we do know or think we know but equally there is lots of solid contradictory information as well. I will not go into that here as it would become to “technical” other than saying that American shad would appear to be a remarkably adaptable fish, more so than any other species I can think of

as for the intended fisheries back in the 1800’s, they were an unmitigated disaster. No market mostly here in the west, and no shad sport fishing tradition, so in that respect a total waste of time and effort. With the improved forms of transport and cold storage since then it would in theory be possible to service a market back east now but there is another problem: American shad’s necessity for spawning to take place in a narrow water temperature band. This means, or rather has meant, that American shad returns to say the Columbia system at the same time and the same locations as the heavily regulated and protected summer Chinook and Sockeye salmon, so harvesting shad in any numbers under those conditions is “not on”. Interestingly the shift in water temperature we have been seeing over the past decade to warming earlier in the season, is leading to American shad spawning earlier, but this time with spring Chinook, equally protected and regulated, and therefore still no potential for a commercial fishery. What is remarkable though is that this time shift has taken place at all; the salmon have stuck rigidly to their typical time slot, irrespective of water temperature. Another piece of evidence of the remarkable adaptivity of American shad.

it is this ability to adapt that fascinates me so much and at the same time irritates me so much as there is absolutely no concerted effort to study this adaptive capacity of shad in the Pacific let alone compare it to the current state of the original Hudson populations. Absolutely incredible as far as I am concerned, as if there is one fish that can give us any inkling as to what climate change is going to mean for marine fish populations and why, it seems to be American shad and here in the Pacific….

fortunately for me however I have a friend who is a fisheries observer and who is now collecting some data on captured shad as a by-catch to satisfy our joint curiosity. Data which already seems to turn some of the things we “know” on its head. Only a very small project but at least a beginning. So we may learn a little bit more about what I think of as Seth Green’s finches, American shad in the Pacific and its ability to adapt, maybe through natural selection or maybe because it doesn’t care and can cope with whatever we throw at it anyway… sooner or later we will find out; just let’s hope someone on the East Coast gets as interested as we are…