News

Time to catch up on a few items on the fish front.

Sharks may be worth more alive
than dead

A shark in the bush (so to speak) may be significantly more valuable than a shark in the hand.  A study published recently in Oryx - The International Journal of Conservation and using data from 70 sites in 45 countries estimates that shark-related ecotourism brings in over $300 million dollars annually, and that the value of the industry may more than double over the next two decades.  Contrast that to $630 million, the estimated value of global shark fisheries - and throw in the fact that value of those fisheries steadily declining. The takehome - leave those sharks alone.  Shark-related tourism in the Caribbean alone leads to over 5,000 jobs and produces over $100 million in revenue.

The lookdown, Selene vomer

In the new Proceedings of the National Academy of Sciences, we hear about new ideas related to fish camouflage in the open ocean.  Traditionally, it has been believed that a fish's best strategy in open water has been to make itself less visible by using a mirror effect, reflecting sunlight to allow the prospective predator or prey to blend into the background.  New research suggests that this strategy, while effective in some circumstances, does not work well in others.  This is particularly true when light penetrating the surface is polarized.  Turns out that many fish species are sensitive to polarization, and the the nature of polarized light is constantly changing.  This means that a mirror strategy won't always be the most effective camouflage.

The authors of the PNAS paper observed lookdowns (Selene vomer), and found that the fish were able to change the way in which light reflected from their bodies in a manner that approached the optimum with regard to camouflaging themselves.  In some light situations, that meant acting like a simple manner.  At other times, the reflected light was altered so as to make the fish less visible in a polarized environment.  It's unclear if the process is passive, with the skin of the fish responding to the available light, or if the fish or somehow activity changing the way light is reflected.

In the Prehistoric Fish o'the Day category, a paper appearing in Geodiversitas describes a new species of acanthodian which lived during the Devonian some 408 mya.  The fossils, discovered in Eastern Spain, are mainly from juveniles with none from fish larger than a meter in length.

Acanthodian

The acanthodians, sometimes referred to as "spiny sharks", were among the first of the jawed vertebrates.  They were characterized by a series of stout spines in front of all the fins.  Many of the early acanthodians had two rows of paired ventral fins.  This makes them particulary interesting to students of vertebrate evolution, as the rows of fins have been suggested (through the fin-fold theory) to have paved the way for the evolution of paired fins and, ultimately, limbs.