The Developmental Stages (Ontogeny) and Associated Habitats of Common Snook

Snook fish in their habitat

In trying to understand how important a particular habitat is to the survival and well-being of any stock of adult fish, it is daunting to realize that some portion of any aquatic environment is essential for the growth and survival of a particular life stage of any given fish species.

Thus, it becomes extremely difficult to assign a value for a single habitat for a single life stage of any fish, especially for snook because each of their growth stanzas occurs in a different habitat.

However, the results of over 50 years of research by numerous biologists concentrated on the requirements, characteristics, and measurements of the habitats occupied by snook less than a year old, snook that are immature pre-adults, and adult snook have demonstrated that some habitats are more important than others.

From these decades of applied research, we have found that the magnitude of the survival of the juvenile young-of-the-year (YOY) contributes significantly to the level of abundance of the adult population.

The equation or model for snook is difficult to understand because the YOY require and live in a completely different habitat with different physical and chemical attributes than do the adults, even though both life stages may share, and compete for, identical habitat during certain months, and even for entire years under certain conditions.

Adult snook can and do live in almost any habitat as long as the physical parameters are not detrimental to life, i.e., the water must be of moderate to good quality- not anoxic, not hypersaline, nor of extreme temperature.

To wit, one may find adult snook around docks and wharves, in canals, along seawalls, under moored watercraft, in dredged water-control ditches, inside mosquito impoundments, inside commercial ports, alongside well-lit waterfront restaurants and boardwalks, and obviously in rivers, estuaries, and on nearshore reefs.

Adults then can live in many man-made or altered localities.

However, there are limitations- construction activities such as dredging, driving piles, trenching, and natural disturbances from hurricanes and red tides will displace snook from their normal lairs.

If the physical and chemical attributes of the area have not been severely altered, then snook will return to these locations after a hiatus of several days up to several years.

Additionally, one of the most enigmatic postulates in fisheries science is that the relationship between the magnitude of the recruitment of juveniles into the adult stock is not directly related to the total number of reproducing adults in that stock.

What we do know is that high levels of successful recruitment of healthy juveniles into the adult stock are related to the condition and magnitude of the larval and juvenile nursery habitats.

It is the habitat utilized by the larvae and juveniles that supports the first year of growth that is so critical in the life cycle of snook.

The habitat and its’ condition provide shelter from predators, ready sources of food, and a stable set of environmental parameters that allows the diminutive form to conserve energy and invest the profit into growth.

There are two life stages that occur in a snook’s life cycle during the first 10-18 months after hatching that require their own unique habitat to support the individual’s development until it recruits into the successive stage or into the adult population.

Larvae, the first stage, occur within the mangrove swamps and bayous, or ‘mangrove fringe, ’near coastal inlets and secondary bays where mangroves proliferate and where most snook are spawned.

The second life stage is the young juvenile (YOY), a snook that has lived through the larval stage but is not yet sexually mature, that is found in the low-saline portions of the high estuary and into the adjacent freshwater portions of creeks, rivers, and lakes.

The larval stage commences immediately after the fertilized egg hatches. Fertilization is a product of spawning that usually takes place near coastal inlets and river mouths where the salinity is greater than 27-28 parts per thousand (ppt).

This high salinity, almost sea-water which is 36 ppt, is required to keep the egg afloat. In less saline waters, the egg would sink to the bottom and fall victim to bacterial invasion.

It may be possible for common snook to spawn or shed their gametes in other areas where required conditions are met; however successful reproduction, i.e., the culmination of living larvae, can only occur in waters with appropriate salinities greater than 28 ppt.

The fertilized zygote remains in the egg for about 24-28 hours during which time it becomes entrained in prevailing tidal and wind-driven currents and a large portion of the clutch is transported into the nearest bay or alongshore into the adjacent estuary, depending on the direction and phase of the local tides and winds.

For the first 2 to 3 days of life after hatching, the larvae float passively suspended in the water column within the lower and middle reaches of the bay.

At about day 3 the larvae metamorphose into a more fish-like form, termed the flexion stage, that has a well-developed tail that is used to actively swim and the net movement of the remainder of the clutch is into, and they settle out in, the fringing, quiet, backwater mangrove habitats near or adjacent to the coastal inlets, rivers, and barrier islands.

This larval nursery must provide a quiet location that is protected from fast currents or vigorous wave action because fishes of this size are extremely fragile and are easily damaged or killed by the slightest turbulence.

This home, must have good water quality, provide sufficient cover from predators, have an adequate food supply of small planktonic copepods, mysids, worms, and insect larvae that are sufficiently small to fit the gape of the young snook’s mouth (usually < 1/16”), and have a direct pathway to nearby waters of lower salinity and even freshwater.

The larvae metamorphose into mini-adults (referred to as post-larvae by many authors) at about day 7 and remain in these same fringing mangrove habitats for the next 45-55 days, during which time they grow to about 2 inches (45-55 mm) in total length.

Their diet consists totally of planktonic invertebrates in sufficient quantities to support growth rates of about 0.8 – 1.2mm per day. These types of habitats are abundant and are somewhat protected by virtue of their inaccessibility