Disturbances of harbor seals by oyster boats in Drakes Estero have been the subject of the most heated arguments over the environmental impact of Drakes Bay Oyster Company.
Scientists at Point Reyes National Seashore have for years claimed a correlation, if not a causal relationship, between increased shellfish harvest and decreased seal counts, while oyster farm advocates have blasted that idea.
But the most recent National Park Service data, released after two separate monitoring periods this summer, are out of sync with the agency’s position—which was memorialized in the final Environmental Impact Statement that informed the federal government’s decision to shutter the farm last year.
Seashore scientist Ben Becker said the preliminary data will be finalized in a harbor seal database expected to be completed and posted online this fall. Those data show that harbor seals are thriving along Marin’s coast this year, and nowhere are they happier than in Drakes Estero.
Historically, counts are highest at Drakes Estero and Double Point, and this year’s counts are not aberrant.
But at the same time, oyster production in Drakes Estero is on track to meet what oysterman Kevin Lunny said will likely be an all-time high in the nine years he has run the farm.
Mr. Lunny, who worries that the EIS not only casts a negative light on his own op-
eration but also could be used against other oyster farmers, believes the new data should prompt another look at the longstanding claims.
“I think the record needs to be corrected,” he said.
This year’s monitoring during the molting season provided weekly counts of seals at five sites—Bolinas Lagoon, Double Point, Drakes Estero, Tomales Bay and Point Bonita—over a period of four weeks when the animals shed their hair after breeding. “The combined total of each site’s peak count was 3,888 seals. This is the highest count since 2006!” it enthusiastically states.
The counts, tallied by trained volunteers, are taken during low to medium tides from fixed observation points.
Drakes Estero had the highest peak of all in 2013, with 1,122 seals one week; Double Point had the next highest, with 1,012 seals another week. The peak in Drakes Estero was higher than its 2012 peak of 701 seals and 2011 peak of 576.
A separate park service document from May, which tracked counts of only pups, showed that the peak count at seven sites in Marin during a two-week period was “the highest it has ever been in all the years of this monitoring program!” Counts were highest at Drakes Estero and Double Point, with 333 and 441 pups, respectively.
The problem for the hypothesis that oyster farming detrimentally impacts harbor seal populations is that Drakes Bay Oyster Company’s production in 2013 is likely to hit the highest yield since Mr. Lunny took over.
The farm yielded about 585,000 pounds of meat in 2010; 620,000 in 2011; and 530,000 in 2012, according to oyster farm records. Mr. Lunny estimates that 2013 will yield about 650,000 pounds.
Yields depend greatly on the survival of oyster seed and environmental conditions, so even the same amount of seed planted can result in greatly varying results. In addition, increased harvesting does not neatly correspond to increased boat traffic.
If there is more work to be done on a boat trip, Mr. Lunny explained, “We put another person on the boat.”
In an analysis by park service scientists Dr. Becker, Sarah Allen and David Press, published first in 2009 and modified multiple times, high oyster production levels were correlated with lower maximum pup counts. The report, commonly known as the Becker report, was subsequently cited in the Environmental Impact Statement, which concluded that continued oyster farming would lead to moderate adverse long-term impacts on harbor seals.
But data gathered after 2009, the last year used in the paper, do not appear in line with that correlation.
In 2010, for instance, the maximum pup count was 220 pups, when oyster production was about 585,000 pounds. But in 2013, when Drakes Bay’s bivalve production is likely to yield 650,000 pounds, the maximum pup count is also higher, at 333. Or take the 2011 numbers, when production was not much higher than in 2010, but the maximum pup count was over 360.
Corey Goodman, a Marshall resident who has been an outspoken critic of much of the science associated with the oyster farm, ran a linear regression for the Light of maximum pup counts and oyster yields between 2005 and 2011, as well as for 2013 (2012 pup counts have not been released). Dr. Goodman found no statistically significant relationship.
Molting season seal counts do not always reflect pup counts, and it is difficult to say what causes the variations. In 2012, a year when pup counts were healthy but molting counts were low, the park service hypothesized that seals could be out foraging for food, could be molting elsewhere, could have been disturbed, or could be affected by “some other unknown factor.”
The Becker report did not analyze seal counts during the molting season, but the increase in those counts in 2012 and 2013 at the same time oyster production was increasing brings into question whether the farm indeed has an adverse impacts on seals.
A Marine Mammal Commission report, published in late 2011, found that the data in the Becker report were “scant and stretched to their limit,” but that the analyses “provide some support for the conclusion that harbor seal habitat-use patterns and mariculture activities in Drakes Estero are at least correlated.” Still, “carefully guided study” would be needed to show a causal relationship.
Many panel members, in their individual reports, expressed serious questions about using mariculture production as a proxy for activity, since, among other things, it does not necessarily reflect planting or boating activity in the previous year or years.
One member, Steven Jeffries, a marine mammal expert for the Department of Fish and Wildlife in Washington state, noted that dynamics influencing California harbor seal populations as a whole and oceanographic events could affect populations in the area.
Brian Kingzett, another panel member and a shellfish research director in British Columbia, took a particularly strong stance against the correlation, writing in his own report, “it is irresponsible at best to make the statement (Becker) that for every 100,000 lbs of oysters harvested there will be 19 less pups and 71 less adults implying that the observed correlation is causal or linear.”
Michael Tillman, a commissioner for the MMC, told to the Light that his agency is not interested in revisiting the issue, despite the recent data. “Time has marched on… Have we accounted for [additional data points]? No, we’re not responsible for analyzing this information,” he said. “We’ve moved onto other higher priority things.”
Dr. Goodman concluded, based on his own analysis of the data, that the correlation between oyster harvest and seal counts was based on a particularly malevolent elephant seal that killed at least 40 harbor seals in 2003, which subsequently led to elevated numbers in Drakes Estero as others sought refuge. The event came during a period when the farm’s previous owners’ were winding down production, so shellfish production was low.
Although seal counts in Drakes Estero continued to decrease after the murderous elephant seal incident, those decreases were consistent with regional decreases, he said.
Mr. Lunny said his boats and workers stay “hundreds of yards away” from the seals, though they are only required to keep a minimum distance of 100 yards.
Many members of the MMC panel said in 2010 that seals habituate to noise when they do hear it. Additionally, a 2006 paper co-authored by Ms. Allen on the effect of Richmond Bridge construction on harbor seals said that seals habituated to loud noises, include nearby bridge construction that involved jackhammers and boats.
Mr. Kingzett said that in his work he’s seen seals calmly hauled out within 50 or 60 feet of shellfish workers.
Tying oyster yields to harbor seal populations ostensibly relies on the assumption that mariculture activity bothers seals; but as the MMC report itself notes, motorboat disturbances comprise a relatively small proportion of disturbances of seals.
During March-to-May periods between 2000 and 2009—the first half of which the farm was under previous ownership—only 10 disturbances were attributed to motorboats. In comparison, birds were responsible for 38 disturbances.
In the most recent disturbance data the Light could locate, from a 2011 park service report, there were 21 recorded disturbances in Drakes Estero during the monitoring season, most of which were caused by hikers. It did not say how many, if any, were attributed to motorized boat activity.