Solving the mystery of the mysids
The summer of 2010 was a remarkable field season for the Earthwatch expedition Whales of British Columbia, with extraordinary happenings that none of Dr William Megill's team had anticipated. The productive, plankton rich waters around Vancouver Island are ancient summer feeding grounds for the grey whale, but since 2004 there have been catastrophic declines in the number of whales observed each year.Dr Megill's team have directly linked this to a decline in abundance of small, shrimp-like crustaceans known as mysids, which are a key whale food source. The effects of this crisis were felt to such an extent that in 2009, mysids had completely disappeared from some areas, forcing the whales to go further offshore to feed, sifting through sand to find other sources of food. This clear downward trend in whale and mysid populations meant that findings in 2010 came as a complete shock to the scientists, because not only had the mysids returned, but they had returned in such abundance that they brought record numbers of whales back to the area.
Grey whales face an uncertain future.
This puzzling result has sent scientists back to the drawing board, and raised more questions. What caused the mysid crisis, and why did they reappear so dramatically? The team are looking for more clues in California, where the whales continue their migration.
Grey whales (Eschrichtius robustus) were taken off the endangered species list (IUCN Red List) nearly 20 years ago thanks to the removal of the threat of commercial whaling, but there are still grave concerns over their future, and individual groups still face considerable threats. This research takes place on the key migration route for a group of grey whales known as the Southern Feeding Aggregation. The migration route extends for around 5000 miles along the west coast of North America, from the breeding lagoons in Mexico's Baja California to feeding grounds high up in the North Pacific. The Earthwatch project sites at Clayquot Sound and Cape Caution in British Columbia are part of the grey whale's principal summer feeding grounds, where the cool, nutrient rich waters play host to a productive ecosystem with abundant food.
The area's whale population is directly related to the amount of food available. If there is no food, whales are forced to look elsewhere, and resort to foraging through the sand and mud further offshore, or migrating even further north in their search for food.
Just last year, Earthwatch reported that the worrying decline of mysids in the waters of British Columbia was fast becoming a crisis for the grey whales. In one area, grey whale numbers had fallen from more than 100 individuals in 2004 to only three in 2009. Earthwatch scientists and volunteers aboard the Stardust research vessel surveyed transects throughout the Pacific waters of Vancouver Island, and could not identify any other grey whale areas. This led to their conclusion that that the majority of the whales making their migration had been forced northward in their search for food. Those that remained were forced to make very different use of their habitat, moving to open waters and foraging along the seabed.
The research is taking place in both Canada and California.
Fears for the consequences of this food shortage were confirmed by the team's colleagues in Mexico studying the whales' breeding and wintering grounds at the other end of the migration route. Scientists at Baja California reported increasing numbers of ‘skinny' whales, and the spring of 2010 saw an unusual number of whales stranded along the west coast migration route.
Although it is clear to scientists that the main cause of the mysid decline was their consumption by whales, they cannot yet explain why their numbers did not return for the next season, as they had done without fail for years. Finding the elusive explanation for this has been made even more complex by 2010's dramatic results of an unprecedented population increase, and current theories of whale/mysid population cycles do not seem to fit these new results.
In one word, lead scientist Dr William Megill can only describe the results of 2010 as "wow". Record numbers of whales were observed continuously throughout the season, with more individuals sighted than in any season over the last two decades. The reason for the abundance of whales is clear; the mysids that Dr Megill and his team assumed were "on the way out" in 2009 had returned with spectacular force in mile-long swarms. Underwater cameras revealed that these swarms were thick enough to impair visibility, and sonar data is currently being processed to allow the team to map out mysid hotspots.
Volunteers at work in British Columbia.
Data processing is still at an early stage, so no analytical conclusions can yet be drawn as to what has caused this increase, but it is clear to the team that something ‘went right' with the productivity of the British Columbian waters this season. To find more clues to this puzzle, the team are developing overwintering studies both in British Columbia and in California. Whilst the weather allows, scientists remaining in Canada have already begun gathering winter data to determine the rebound effects from such a plentiful summer. In California, teams are currently setting up, ready to gather data on the whale migration for this leg of the journey, which will hopefully shed vital light on the complex factors which govern the migration.
Answers in California?
This exciting new phase of the research is being expanded with one of the team's scientists, Dr Lei Lani Stelle, from California's Redlands University. One of the key aims here is to record data such as swim speeds and respiration patterns on the whales passing the Palos Verdes Peninsula area in California, to determine what effect the dramatic events in the Arctic are having on the whales' physiology and energy use during migration. On this stretch of their route, the whales are also in greater direct contact with human activities including major shipping lanes, whale watching boats, oil rigs and pollution, and Dr Stelle's work aims to examine the extent of these impacts as well. Thanks to the wealth of photo-identification data collected in British Columbia, it will also be possible to determine known individuals as they make their way along their migration and paint a more detailed picture of how these mammals live.
Find out more about how to join the Whales of British Columbia expedition.
Dr William Megill will be speaking about his research at the Royal Geographical Society in March. Join us there.
Report by Ellie Gilvin.