Part II. THE PHENOLOGY OF BABY FISH IN LAKES AND PONDS

There is a need to know more about the distribution and occurrence of newly hatched fishes. For example, it is now known that the babies of the common lake whitefish and lake herring live at the surface of lakes in early spring. Imagine how many of these are killed when a 100 hp outboard motor goes across a lake. All young fish are not found along shorelines, in weed beds, or even in shallow water. In fact, one reason why so few baby fish are known intimately is because many live in deep water even though they hatched from eggs laid in shallow water. Neither adult nor baby fish live just anywhere, for, like deer, rabbits or warblers, each species lives within a definite habitat within "their" range. Biologists are gradually learning where baby fish live. A thorough knowledge of their whereabouts from egg through larva, juvenile and into adult is known for surprisingly few species. Readers should be reminded that fishes are unique among all vertebrates - no other vertebrate order has its babies occupying so many different habitats and displaying such widely diverse anatomical features. A good book on the early life of a fish is: The Angelfish: Its Life Cycle (White and White, 1979).

Fishermen normally expect to find northern pike near weed beds, rockbass in shallow rocky areas, smallmouth bass along deep rocky shores, and so forth. Such differences in habitat and behaviour show a general tendency for fish (and other animals) to restrict the bulk of their activities to particular portions of their available range. So it is with baby fishes, except that these habitats are usually different from where their adults live. The search for young fishes must not be biased by knowledge of their adult behaviours. The active or passive movement of newly hatched fishes away from places where they are hatched is important. Different species of baby fishes live in different parts of lakes.

Certain species of baby fish display completely passive behaviour while others show active dispersive movements. At times, passive larvae are carried by wind-driven currents into the offshore weedless region (pelagic or limnetic region), while at other times they remain quiet among shoreline vegetation. On the other hand, it is those species with dispersive swimming movements or innate "wanderlust" that are so difficult to find. Baby fish which remain within shallow littoral regions possess darker patterns of pigmentation than those that disperse away from shallow waters. One theory says that those larvae restricted to shallow water need the extra pigmentation for protection against normal rays of the sun; those restricted to deep offshore waters can protect themselves without pigmentation by swimming into deeper water where light intensity naturally diminishes. Another theory says that larval fishes adapt to their immediate environment; that is, those living in dark, shady areas develop dark patterns of pigmentation while those living in open, lighted areas do not develop dark pigmentation.

Shallowwater babies or darkly coloured ones, which are relatively easy to locate and see, include: pikes (Esocidae), bullheads (Ictaluridae), suckers (Catostomidae), sticklebacks (Gasterosteidae), most minnows (Cyprinidae) and basses (Centrarchidae). Deepwater babies or lightly coloured ones, which are usually difficult to see, include: yellow perch (Percidae), sunfishes (Centrarchidae) and rainbow smelt (Osmeridae).

Phenology of Larval Fishes

In every body of water there is an unseen phenology of baby fish species; that is, various kinds come and go. This succession or seasonal occurrence is, of course, the result of different hatching times. Since the eggs of different species have different incubation periods, actual spawning times are only indirectly related to phenology. Temperature is a controlling factor, and annual changes in the rate of lake warm-up effect fish spawnings. The warm-up of lakes is affected directly by air temperatures; therefore, cool springs delay hatching, whereas warm springs hasten hatching. On the other hand, the sizes of lakes also temper baby fish phenologies. As an example, yellow perch babies occur in May in shallow lakes which warm up quickly, whereas they occur in June in deep lakes which warm up more slowly. Annual differences in phenology are detectable only with a regular field sampling program for fish eggs and larvae.

A calendar of baby fish phenology for several species in the Ottawa-Carleton region in Ontario is shown in Figure II-1 (below). This calendar is subdivided into two groups or habitats where different phenologies exist, those that live in shallow water among aquatic plants and those that live in deep water. Although this is not a complete phenological calendar for all possible species, it shows the seasonal occurrence of many common species. Notice the relationship between water temperature and the first appearance of each species. The "harbinger temperature" is the value of the surface temperature of the water when a particular species of larvae is first collected or available to some particular collecting device. Harbinger temperatures are almost unique for each species.

Scientific knowledge about the distribution and phenologies of baby fishes is finally becoming available. This knowledge is important for the effective management of sport and commercial fishes and for accurate information of our natural resources. Scientific studies which relate directly to these subjects in clude the following: Amundrud et al., 1974; Cucin and Faber, 1984; Faber, 1967, 1980 and 1981; and Werner, 1969.