ACS Research Committee Report

Modeling of Right Whale Entanglement Injuries
Source: Woodward, B.L., Winn, J.P., Moore, M.J., and Peterson, M.L. 2006. Experimental modeling of large whale entanglement injuries. Marine Mammal Science 22(2): 299-310.

North Atlantic right whales, numbering only 300-350 animals in the population, are a severely endangered species. Three-quarters of the population has scars from fishing gear entanglement on their bodies. Entanglement in fishing gear is a serious risk to the survival of right whales, but the mechanics involved in entanglement-related tissue damage is poorly understood.

This study modeled entanglements and the resulting tissue damage using a reciprocating load generator and tissue from a dead stranded right whale. This system modeled the entanglement scenario where one end of the line is fixed and the other alternates load and relaxed states depending on the flexure of the tail during fluke strokes.

The average fluke stroke rate of right whales is 12 strokes per minute, but the model had a rate of 60 strokes per minute (five times that of right whales).

Four types of line were used in the experiment: new and old line made of floating and of sinking material. The new line made visible marks on the skin, but no deep furrows, whereas the old line made significant furrows in the skin. Each line type had a distinctive appearance, which can be a useful tool in identifying the line involved in future entanglements. Oftentimes, the gear itself is gone by the time a whale washes up and the scars or furrows are the only evidence of the type of entangling gear. None of the trials caused breakage of the skin, but it is possible that the use of post-mortem tissue and the storage of these samples may have altered the skin’s natural durability. The scars created during these trials were similar to scars seen on whales that have washed up dead, indicating that this system of modeling is a valuable tool for understanding the mechanism of tissue damage during entanglement.

Does Diving Limit the Brain Size in Cetaceans?
Source: Marino, L., Sol, D., Toren, K., and Lefebvre, L. 2006. Does diving limit brain size in cetaceans?  Marine Mammal Science 22(2): 413-425.

Large brains have a high metabolic and oxygenation cost. The oxygen demands during diving may pose a limitation on the brain size of marine mammals, which is a hypothesis called the “dive constraint hypothesis.”  This hypothesis predicts that relative brain size would be negatively correlated with maximum dive time. Although it has been tested previously, the results have not been conclusive.

This study examined 23 species of cetaceans for their relative brain size, body size, and maximum dive duration. Several measures of brain size were used: 1) brain to body size ratio; 2) Jerson encephalization quotient; 3) Martin encephalization quotient; 4) and 5) log transformations of 2) and 3); and residual brain size.

The maximum dive duration was negatively correlated with all of the measures of brain size, except the residual brain size, which showed no correlation. The residual brain size was the only measure used that did not take body size into account at all.

A multiple regression was performed including body and brain size; the result was that the only significant predictor of dive time was body size. These results lead to the conclusion that brain size does not limit dive time. Instead, maximum dive time seems to be determined by body size and muscle mass. 

Right Whale Distribution in Relation to Sea Surface Temperature
Source: Keller, C.A., Ward-Geiger, L.I., Brooks, W.B., Slay, C.K., Taylor, C.R., and Zoodsma, B.J. 2006. North Atlantic right whale distribution in relation to sea-surface temperature in the southeastern United States calving grounds. Marine Mammal Science 22(2): 426-445.

In order to protect right whales, it is imperative to understand their distribution and how it is affected by oceanographic conditions. There have been many studies in the feeding grounds that have correlated right whale distribution to features such as bathymetry, sea surface temperature, and thermal fronts. It is assumed that these features actually affect the prey base, which secondarily affects whale distribution. There is much less known about the distribution of right whales on their calving grounds in the southeastern United States. The environmental cues that initiate migration are also poorly understood.

This study correlated sightings of right whales from aerial surveys off the coasts of South Carolina, Georgia, and Florida in the period 1991 to 1998, with sea surface temperature measured both remotely via satellite and in-situ via a moored buoy system.

Sightings were broken into four zones, going from north to south: Georgia near shore, Early Warning System (EWS-off the coast of southern Georgia and northern Florida), offshore, and Florida near shore.

Right whales were found in a relatively consistent range of temperature and their distribution was not random amongst waters of different temperatures. In February, whales were located in the southern part of the EWS zone in waters that were warmer than the search-area mean. During December and March, however, whales were seen at higher and more variable latitudes and temperatures, as may be expected due to migratory behavior. Sea surface temperatures were warmer in the Florida near shore zone than in the EWS zone and they increased throughout the winter calving season. In January and February, the temperatures around whale sightings were found to be lower than the average for the search area; whales were observed more often in the northern, cooler part of the Florida near shore zone.

The overall mean sea surface temperature for whale sighting locations in the study was 14.3ºC. This mean plus two standard deviations is approximately 20ºC, which represents an upper value of right whale distribution that only a small percentage of sightings would theoretically exceed. This upper value corresponds to that used to define the location of the Gulf Stream, indicating that this current may be an upper thermal limit to the distribution of whales during the calving season. The Gulf Stream is close to the shoreline in southern Florida, but it shifts to the east through northern Florida and Georgia, leaving a wedge of cooler sea surface temperatures that the whales use during the calving season. Right whale critical habitat is located mostly within this wedge of cooler water. The Gulf Stream may provide a southern and an eastern boundary for right whale use during this season.   

 

Support ACS's public education programs - Join Today