Here you go Bob,
â€œActually, Patarero, you haven't refuted anything. All you've done is mouth absurd allegations that the Ransom paper was "full of invalid assumptions and holes" without providing any specifics or relevant argument. â€œ
The list is so long I didnâ€™t have time to go through it all last night
â€œNot only have shark numbers declined, the paper notes multiple surveys showing increase in population of cownose rays by an order of magnitude since the mid-1970s, as well as growing numbers of other "mesopredatory elasmobranch prey" of great sharks. The trophic cascade argument developed in this paper attributes depletion of bay scallops in the Chesapeake to increased predation by cownose rays.â€
Bay scallops in the Chesapeake were wiped out by the loss of eelgrass and hurricane Agnes (1933).
â€œWhether the "commercial guys" in Chesapeake Bay think rays eat oysters or not isn't relevant to the claims of this paper. The paper states that cownose rays diet "consists largely of bay scallops (Argopecten irradians), soft-shell clams (Mya arenaria), hard clams (Mercenaria mercenaria), oysters (Crassostrea virginica) and other noncommercial bivalves, citing an article by Robert Blaylock (at the Virginia Institute of Marine Science of William and Mary College) in Estuaries, "Distribution and Abundance of the Cownose Ray Rhinoptera bonasus in the Lower Chesapeake, and also citing a thesis by Donna Grusha. Even if your opinion (since you cite no evidence) that the cownose ray mouth morphology makes it "virtually impossible" for the ray to eat oysters happened to have any validity, the arguments made in this paper relate to the precipitous decline in bay scallops (A. irradians), not oysters. â€œ
This was in response to the proposed fishery to market cownose rays in Asia, not related to the paper. Have you ever seen a cownose ray eat? The mouth morphology is not like many of the other stingrays. Have you read Blaylocks paper? It is on abundance of the cownose ray in the Chesapeake through aerial surveys. Not 1, not a single cownose was caught and examined to see what they were eating. In the paper it states Mya arenaria is the preferred prey citing other documents. It further states
" Although Merriner and Smith (1979), Smith (1980), and Smith and Merriner (1985) reported Mya arenaria to be its perferred prey, oyster planters in Virginia have reported larger losses of planted seed oysters to foraging cownose rays during the summer (personal comm. commercial seafood wholesaler). ....Meriner and Smith(1979) speculated that an increase in cownose ray predation on privately leased oyster beds in Virginia was attributable to "the destruction of Mya stocks in the Rappahannock River due to tropical storm Agnes 1972 and the catastrophic decline of oyster production in the Chesapeake Bay over the past 25 years."
â€œThe Myers paper doesn't just infer a linkage between ballooning cownose ray populations and the collapse of bay scallops. "Analogous recent sampling, confirmed by controlled ray-exclusion experiments using stockades, demonstrates that since 1996 migrating cownose rays have caused almost complete scallop mortality by early fall ... at every site with initial adult scallop densities above a threshold for intensive ray foraging (~2 m-2)." The authors further note that, having essentially depleted the bay scallop population, "increased predation by cownose rays ... may now inhibit recovery of hard clams, soft shell clams, and oysters, compounding the effects of overexploitation, disease, habitat destruction and pollution, which have depressed these species," but at no point in their paper whatsoever do they ever state that cownose ray predation has been a major factor in the decline of oyster and other bivalve populations to date.â€
This is in the first papragraph:
â€œEffects of this community restructuring have cascaded downward from the
cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a
century-long scallop fishery. Analogous top-down effects may be a predictable consequence of
eliminating entire functional groups of predators.â€
â€œYour views and opinions are welcome, Patarero, but if you seriously want to challenge some of the best marine fisheries science that has ever been done by anyone anywhere, you'll have to do better than just mouth unsupported, ridiculous attacks. For a start, you might try reading the paper next time before you post your own insightful comments.â€
I find the statement â€œbest marine fisheries science that has ever been done by anyone anywhereâ€ particularly offensive and unsubstantiated. What happens when the cownose ray population dives and shellfish landings continue to decline? Was it lack of shellfish, decreased demand, health issues involved with eating possibly contaminated shellfish? This paper will be used to support a fishery for cownose rays, an animal that has the life history characteristics similar to cetaceans.
The data used in the analyses for bivalves are commercial landings. The numbers presented are driven by economics. Besides the fact that these data are driven by market value and demand, bivalves on the east coast of North America have been subjected to disease (msx and dermo) and environmental conditions that have wiped out various markets, especially in the case of oysters.
Furthermore some of the â€œgreat sharksâ€ and â€œmesopredatorsâ€ ranges do not overlap. For example, they include chain catshark. This species is off the shelf of North America (155-545m depth, 8.5-11Celcius) and is rarely if ever encountered by the â€œgreat sharksâ€. Why did they include it, because a different species of the same family comprised a minute percentage of food items of sharks caught in the gill-nets off of Natal, South Africa. The species that the â€œgreat sharksâ€ off of South Africa encounter is Halaelurus lineatus (lined catshark). This species occupies depths from 0-290meters. The occuranceThis is a completely different animal, occupying a completely different region of the ocean. Why was it included? Because it shows the trend they want to show.
Look at the little skate, the only evidence for a â€œgreat sharkâ€ consuming little skates is for the sandbar. Why is this, because it is the only demersal shark species that encounters little skates, the dusky may encounter it on occasion. The great white and mako overlap with the little skate, but they are pelagic predators. Oddly the sandbar shows the smallest decrease in abundance of the â€œgreat sharksâ€, yet the little skate shows disproportionate increases.
Iâ€™m sure the folks that did the last rebuttal to this groupâ€™s work will present another one. If you want to give me a call and discuss it further Iâ€™ll shoot you my number.