Large female fish produce a disproportionate number and more robust eggs than previously thought, according to a new study published in the journal Nature.
As recounted in an article in the Washington Post, biologists at Monash University in Australia and the Smithsonian Tropical Research Institute in Panama gathered egg data from 342 fish species across the world’s oceans.
At the extreme end of the spectrum, the vermillion snapper had a 400-fold difference between the smallest and largest of females. A small snapper lays about 4,000 eggs, while the largest specimens lay eggs by the millions, according to the study’s authors.
While every halibut and cod fisherman is aware of the obviously higher egg count in large females, what is less known is how much more productive those eggs are. The study used the example of cod, noting that a 66-pound cod will lay more eggs than 28 4-pound fish. In other words, it takes more than 128 pounds of small cod to lay the same amount of eggs as one 66-pound fish.
While that may not come as a surprise, what the study also uncovered was the corresponding increase in egg quality. Large females do not simply lay more eggs, their eggs are larger and richer in fat. Based on the “total nutrient content,” the number, volume and nutrients, that 66-pound female actually produces the same amount of offspring as 37 small fish.
The study’s authors, Diego Barneche and Dustin Marshall, told the Post that some fisheries biologists have been advocating for reducing the number of large fish allowed to be removed for some time, especially on the West Coast, but their contribution was to show that the outsized value of large females is “the rule, not the exception.” Some fisheries have started to use egg output as a metric for management instead of weight.
Slot limits are also an important tool, but really are only practical in recreational fisheries. Because fish in marine protected areas tend to grow larger, the study authors said that areas off-limits to fishing could be even more important than predicted.
There are several marine protected areas in Alaska, including the Sitka Pinnacles off Cape Edgecumbe that has been closed to bottom fishing and anchoring since 1999.
Former president Barack Obama created the largest marine national monument on the planet under his administration, expanding an existing area around the northwestern Hawaiian Islands to 582,000 square miles.
Cristy Fry can be reached at firstname.lastname@example.org.