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Big Old Female Fish – the future of our fishery!

Big, female snook make huge contributions to future fish stocks—Ralph Allen, King Fisher Fleet Image

Big, female snook make huge contributions to future fish stocks—Ralph Allen, King Fisher Fleet Image

Most anglers understand we have two snook closures annually; each for very different reasons. The December through February closure protects snook during the cold weather and the May to September closure protects spawning snook. The size limits for snook are designed to protect juveniles and older spawning female snook. Many people understand the reason to protect juveniles; after all they are the future generation. But why protect the old girls?

Well it turns out size matters when it comes to fish spawning. That’s right Big, Old, Fat, Fecund, Female Fish or BOFFFFs contribute far more to future fish stocks than their smaller, younger same species representatives, and the old girls contribute in many ways.

A 24-inch female red snapper will produce as many eggs as 212 17-inch female red snappers—FSG Image

A 30-inch female red snapper will produce as many eggs as 100 13-inch female red snappers—FSG Image

BOFFFFs make more eggs – It makes perfect sense, the bigger the fish the more room to store eggs. Bigger females also do not need to devote as much energy into growing as smaller female fish and therefore can devote more energy into making eggs. As a matter of fact, just one 30-inch female red snapper will produce as many eggs as 100 13-inch female red snappers! This same pattern holds true for many species including bluefin trevally, salmon, cod, rockfish and snook.

These snook eggs are at various stages of development, which is indicative of a multiple or ‘batch’ spawner—Jim Locascio, Mote Marine Laboratory Image

These snook eggs are at various stages of development, which is indicative of a multiple or ‘batch’ spawner—Jim Locascio, Mote Marine Laboratory Image

BOFFFFs make bigger eggs – There’s a body of research that demonstrates a very positive correlation between female size and egg size. Bigger eggs produce bigger larvae and bigger larvae are more resistant to starvation and predation. Why is this? Well, bigger eggs have a bigger yolk which equates to more food for the developing offspring. A study that looked at egg size on development of walleye determined that larvae from larger eggs had faster hypural bone (bone at the tail) formation and greater body lengths measured one and 13 days after hatching. They also ingested more food, had fewer deformities and lower mortality.

Red snapper eggs at various stages of development. The bigger eggs are more hydrated and buoyant than the smaller eggs—FSG Image

Red snapper eggs at various stages of development. The bigger eggs are more hydrated and buoyant than the smaller eggs—FSG Image

BOFFFFs produce more buoyant eggs – During the final stage of egg development in most marine fishes, there is a massive uptake of water. This increase in water is a survival adaptation that makes the eggs of pelagic spawning fish neutrally buoyant. Being neutrally buoyant helps eggs released into the water column reach suitable habitat for optimal growth and survival. In the case of cod, one of the most studied fish, older females produce more buoyant eggs. In fact, neutral buoyancy is almost six times greater for a six year old fish than a three year old fish at a brackish salinity of 15 (half seawater strength).

BOFFFFs distribute their eggs far and wide – With age comes wisdom, and in the case of BOFFFFs the ability to spawn over longer periods in the season. Not only do old females produce eggs in greater numbers and at a greater size, they also spawn in more batches over extended seasons than do smaller females. This means the big girls are spreading their eggs over many locations and habitats.

There is a growing concern for fisheries where BOFFFFs are not protected. Not only is this bad for future stocks, but it may have far greater implications. By removing the bigger spawning females, we are selecting for smaller spawning fish who produce fewer offspring that are less fit with a slimmer chance of survival. Over time this means fewer adults spawning fewer fish. A cycle like this would be very hard to reverse. So, the next time you catch a BOFFFF treat her with extra special care. She is the future of our fishery.

Sources:

Hixon, M., D. Johnson, and S. Sogard. 2014. BOFFFFs: on the importance of conserving old-growth age structure in fishery populations. ICES Journal of Marine Science 71(8), 2171–2185.

Kamler, E. 2005. Parent-egg-progeny relationships in teleost fishes: an energetics perspective. Fish Biology and Fisheries 15 399-421.

Porch, C.E., G.R. Fitzhugh and B.C. Linton. 2013. Modeling the dependence of batch fecundity and spawning frequency on size and age for use in stock assessments of red snapper in the US Gulf of Mexico waters. NMFS, SFSC, Miami, FL SEDAR 13-AW report. 20pp.

Rhody, N., C. Puchulutegui, J. Taggart, K. Main and H. Migaud. 2014. Parental contribution and spawning performance in captive common snook Centropomus undecimalis broodstock. Aquaculture 432: 144-153.

Vallin, L. and A. Nissling. 2000. Maternal effects on egg size and egg buoyancy of Baltic cod, Gadus morhua Implications for stock structure effects on recruitment. Fisheries Research 49 21-37.

Yanes-Roca, C., N. Rhody, M. Nystrom and K. Main. 2009. Effects of fatty acid composition and spawning season patterns on egg quality and larval survival in common snook (Centropomus undecimalis). Aquaculture 287: 335-340.