With migrations of gray whales peaking in mid-January along the Bay Area coastline, now is a good time to have a bit more in depth of a look at the gray whale. This organism’s conservation classification is not straight forward, even though their geographical range is relatively small, as there are different stocks positioned in different geographical locations with different population numbers.
The IUCN red list monitors the abundance of thousands of species and has a classification system with criteria that place species in categories ranging from ‘extinct’ to ‘least concern’. The IUCN listed gray whales as a whole as of ‘least concern’ in 2008 under the grounds that when the two populations in the north Pacific are assessed as a single species the estimated population size is above the threshold for a threatened categorization. Under the IUCN criteria a species can be moved from ‘least concern’ to ‘vulnerable’ when it meets criteria on any of the following; observed population decline of ≥30%, geographical range decline of the extent of occurrence OR area of occupancy, population size characteristics change, and probability of extinction increase.
There is a Western North Pacific stock that has been classified separately as ‘critically endangered’. This sub-population has met the ‘critically endangered’ criteria by fulfilling criteria E or C2aii which are; E: ‘Recent mortality levels continue, based on an extinction probability, to exceed 50% within 3 generations’ and C2aii: ‘a projected continued decline of the subpopulation in combination with a mature population size of less than 250’.
The Gray whale is found in the Pacific Ocean in the eastern and western north pacific only. They have been extinct in the north Atlantic for several hundred years. Gray whales are bottom-feeding specialists that aggregate during the summer to autumn in shallow waters and offshore banks where the benthic and epi-benthic invertebrate communities that they feed on are concentrated. In the winter they spend their time in warmer sub-tropical areas where they mate and give birth to calves. Females and males both attain puberty from 5-11 years. Females usually come into estrus once every two years in late November to early December, ovulating only once each season. Most conceptions occur within a 3 week period at the end of the southward migration. Females invest heavily in their young, with a 7 month lactation period that ends in August. Females are then in anoestrous from August to December.
Because the Eastern North Pacific and Western North Pacific stocks of gray whales rarely intermingle and have different geographical habitats and population sizes from now on they will be referred to separately.
The Eastern North Pacific (ENP) stock has two groups, one summers in the Bering, Chukchi, and Baufort Sea and the other summers further south with a range from coastal Northern California to southern Alaska. They migrate south to winter in two places, the lagoons of Baja California and the Gulf of California (Figure 1).
The Western North Pacific (WNP) population spends summer to autumn in the Okhotsk Sea off the north eastern coast of Sakhalin Island and migrate south to spend winter in the South China Sea, however, the exact location of the wintering ground is unknown (Figure 1).
Whaling shaped the populations of gray whales in both the eastern and western Pacific. This major factor is important to consider when assessing the conservation status because its effects can still be seen today in both population size and genetic diversity. Because the gray whale uses coastal habitats extensively it was especially vulnerable to shore based whaling. This was probably the reason the species was severely depleted before the advent of modern whaling and one of the reasons it was one of the first whales to be protected.
The ENP stock of gray whales has been subject to low levels of hunting for 2000 years or more. The estimated pre-whaling population size of the ENP stock was 15,000-24,000. Since then this stock has been subject to hunting at their wintering grounds in Baja, California and adjacent waters from 1846-1873. In 1885 there was an approximate estimate of 160 gray whales in this stock. The population was driven to apparent commercial extinction by 1893.
Full protection was achieved in 1946 for gray whales under the IWC. This whale population made a dramatic recovery even though to date there is still aboriginal catches from the ENP stock at subsistence whaling levels. The estimated total gray whale catch in this stock was 27,000 whales caught between 1846 and 2008. Today the total number of whales in the ENP stock is around 20,000 individuals.
Surveys from 1967 to 1998 showed that the ENP stock of gray whales increased at an annual rate of about 2.6% reaching as many as 30,000 individuals. Today the total number of whales in the ENP stock is about 20,000 individuals. However, this stock has two sub-populations that summer in different locations. The majority of these whales summer in the Bering, Baufort and Chukchi Sea, however, there is a smaller population contains a few hundred individuals that summers from North California to Southeast Alaska called the Pacific Coast feeding aggregation. The larger, more northerly, summer feeding aggregation (called the larger population from now on) are showing signs of reaching carrying capacity such as high mortality rates in the form of beached whales. The Pacific coast feeding aggregation, on the other hand, numbers only a few hundred individuals.
The WNP stock of gray whales were probably never as abundant as there eastern counterparts, although the actual number is unknown it is thought they numbered anywhere between 1,500 and 10,000. They were subject to whaling by a number of different sources. Japanese hand harpoon whaling occurred between the 16th and 19th century. Russian steam whalers in the coastal waters of the Far East took whales at the end of the 19th century. European and American whalers took whales in the Okhotsk Sea from the late 1840’s to the early 1900’s. The main reduction in whale numbers came in the 1890s-1960s when Korea and Japan commenced modern commercial whaling, which was a more effective method of hunting whales. Although the gray whale has been protected since 1946 by the International Conservation for the Regulation of Whaling, Japan did not join the IWC until 1951 and the Republic of Korea did not join until 1978. To date North Korea still hasn’t joined the IWC and nothing is known about whaling in its waters since the end of World War II. By 1910 it was estimated that 1,000-1,500 whales remained in this stock. Since then the catch rate of gray whales has declined. It has been hypothesized that the continued low level hunting between the 1940s and 1966 is what hindered the recovery of this stock. It is likely that this stock now has around 90-109 individuals and represents one of the most endangered whale populations in the world.
Life history data has been used to estimate the growth rate of the population and from 1997-2003 they showed an annual increase of 2.5-3.2%. This is a slow rate of increase, and this coupled with the extremely low population size highlights concerns for this stock. Between 1995 and 1999 11 reproductive females and their 15 calves were observed however 58.3% of these calves were not re-sighted. The estimate for the number of mature individuals in the population is 50.
Genetic samples from whales in different stocks can be used to determine whether they are in fact genetically distinct. The ENP and WNP stock of gray whales are geographically isolated from one another. Extensive research has been done looking at the differences of the ENP and WNP stocks and studies have looked at microsatellites markers, genetic and mitochondrial markers and haplotypic diversity. All have found a significant difference indicating genetic isolation between the two stocks. It has also been shown that haplotypic diversity within the ENP is considerably higher than the WNP stock. This information suggests that the ENP stock was affected by whaling much less than the WNP stock in terms of genetic diversity loss which could partly explain the swift recovery rate of the ENP stock.
The ENP stock of gray whales show a complex genetic pattern due mainly to female site fidelity. Comparisons of mitochondrial sequences from the larger population and pacific coast feeding aggregation show significant differences in haplotype frequency indicating the maternal lineage of the pacific coast feeding aggregation represents a distinct summer subpopulation. Moreover, the three specific calving lagoons they occupy in the winter around Baja, California (figure 1) give rise to genetic differences, a small but significant isolation level between Bahia Magdalena and Laguna San Ignacio exists. Researchers have hypothesized that this isolation level would be higher if it wasn’t for the disruption of structure caused by whaling. This indicates that gray whales may return to their natal lagoons, facilitating population isolation.
The WNP stock numbers around 100 individuals and is increasing in population size slowly. This coupled with the life history of the organism (calving once every 2 years, taking a long time to reach maturity) and continued unknown whaling from countries within this stocks range only exacerbates the problem, having said that the stock does show relatively high haplotypic diversity that could be a cause of slight intermingling with the ENP stock. This is why the stock has been given the ‘critically endangered’ classification. The steady increase in population size does go against the criteria of a projected continued decline of the subpopulation however this increase is so slight and the number of mature individuals is so low compared to the criteria, coupled with the persistent whaling problems that have to be assumed to be continuing, mean the subpopulation is far away from coming out of this classification criteria.
The ENP stock has a total number of around 20,000 individuals, however within the stock there are subpopulations that have been shown to be genetically distinct such as the subpopulation of a few hundred that summer from northern California to southeast Alaska, the Pacific coast feeding aggregation. These distinct sites are caused by female site fidelity. As a whole the ENP stock has justification to be classified as of ‘least concern’, showing signs of reaching its carrying capacity however the degree to which this is a single stock has come into question recently and if they are isolated populations, as the genetic data suggests, the Pacific coast feeding aggregation, numbering a few hundred, would have grounds to be reassessed under the IUCN criteria. More research will be required before we know if this sub-population within the ENP stock should be reclassified. Reclassification will have knock on effect for decisions made about aboriginal whaling and conservation priorities so it is important that classification is correct as best as possible.
Written by Matthew Scott
Post graduate marine biologist; spotter of whales; writer for ACS SF chapter; swimmer of oceans; companion to dogs.