As reported earlier, fish populations may adapt and change in response to significant fishing pressure. Researchers are now suggesting that the genetic make-up of cod in the Atlantic Ocean might be changing, since cods genetically predisposition to seek out shallower waters are more likely to end up in nets or on fishing lines, while deep-dwellers are more likely to survive and reproduce.

If the current over-fishing of shallow living cod is not put to an end, evolutionary biologist Einar Árnason and his colleagues believes the genetic variant found in shallow-living cod will be lost all together. If the deep-water cods do not spread into the shallows, and Árnason doubts they will since they are adapted to deep water conditions, the shallows may be become devoid of cod within the next 10 years. This will decrease the size of the total cod population and will also force the fishing industry to either give up cod fishing altogether or switch to expensive deep-water trawling.

Árnason and his colleagues have studied cod populations off the coast of Iceland, where fish stocks are still in fairly decent condition compared to the severely depleted populations found in the western Atlantic. In their study, the researchers examined how the genotypes of Icelandic cod have changed between 1994 and 2003.

It was already known that cod living in the Icelandic shallows have a different variant of the pantophysin I gene than the cods found at much larger depts. In their study, Árnason and his colleagues found that the shallow-water variant of pantophysin I is becoming increasingly rare; a change which they attribute to the fact that most Icelandic cod fishers work in shallow waters near the coastline using lines and nets instead of carrying out deep-water trawling.

Árnason and his team also found that Icelandic cod are reaching sexual maturity at a younger age and at a smaller size than before. This is discovery is a chilling revelation for Icelandic fishermen and conservationalists alike, since that was exactly what happened in Newfoundland waters before that cod population crashed completely.

The study has been published in the journal PLoS ONE

A strange algae plume has turned the normally crystal clear Caribbean Sea around the Virgin Islands green down to a depth of roughly 80 feet (25 metres) and sharply decreased visibility in these popular dive waters. How and if the plume will have any long-term effect on the region’s marine life remains unknown.

Tyler Smith, assistant professor at the Center for Marine and Environmental Studies at the University of the Virgin Islands, said that when he went diving Tuesday the visibility inside the plume was no more than 10 feet (3 metres). Below 80 feet, the water was just as clear as normally.

The reason behind the extraordinary plume can be found in South America, in the Orinoco River which flows through Venezuela before reaching the Atlantic Ocean. When the Orinoco outflow is larger than normal, the vast amounts of nutrient-rich freshwater from Venezuela cause a major algae bloom in the nearby ocean. Mixed fresh- and saltwater is lighter than seawater and will therefore rise to the top of the water column.

“It’s very stable, so it just sits there,” Smith explains.

Carried by currents, the algae plume has now spread from the South American east-coast to the Caribbean Sea and can currently be seen not only off the British and U.S. Virgin Islands but in Puerto Rican waters as well. The first patch was noticed by Smith and his colleagues in the waters off St. Croix on April 9.

When the amount of photosynthesising alga increases in a region, it attracts all sorts of organisms that feed on algae and make it possible for these populations to boom as well. The algae plume around the Virgin Islands supports an entire food chain of marine life, including plankton, jellyfish, crustaceans and fish. It is not dangerous to swim or scuba dive in, but some people might dislike the high density of jellyfish.

“This is an event that occurs every year, but we haven’t seen it come this far north,” says Trika Gerard, marine ecologist with the U.S. National Oceanic and Atmospheric Administration (NOAA). In a stroke of good luck, a NOAA research vessel was scheduled to research reef fish in these waters from April 7 to April 20 – right at the peak of the unexpected plume.

To find out more about how the plume effects marine life, the Caribbean Fisheries Management Council is urging anyone who goes out fishing in the green plume to report their location, target species and success rate of each trip. According to local fishermen the fishing is always awfully bad when the water is green, but this has not been scientifically researched yet and all data is of interest.

You can reach the Caribbean Fisheries Management Council by calling (787) 766-5927. Their website is http://www.caribbeanfmc.com.