1. shoals: groups of fish remaining together for social reasons
2. schools: synchronized and polarized swimming groups

1. visual
2. acoustic (lateral line)
3. these systems interact

blinded fish can still school; those with lateral line sense obliterated can also. In each case ability somewhat impaired/altered.

1. sizes similar
2. usually single species

1. Hydrodynamic advantage
1. theoretical energy savings of 65%
2. precise spatial relationships required
3. savings don't accrue to all members
4. drag-reducing mucus?
2. countering predators
1. There are quite a number of ways that predators might be countered.
2. Note that fish group size increases upon exposure to a predator (p 308 fig 12.5, Pitcher)
3. Avoidance

predator less likely of coming into detection envelope of single group than whole bunch of individuals? careful attention to this concept indicates no advantage; in fact in many cases: shoals more likely to be detected than individuals; shoals often attended by predators

4. Dilution of attack

This one also tricky. If all individuals in an arena have been detected, it makes no difference whether they are in groups or solitary (fig 12.4 B, Pitcher p 304). But an alternative model, in which a predator is searching and has the same probability of finding a group of any size, then attacks within a group, favors joining groups (p 305)

5. Evasion

fish in schools exhibit a number of interesting cooperative avoidance behaviors (fig 12.6, p 309). Reaction to predators propagates v swiftly through school, faster than predator approach speed

6. Pred confusion.

Hard to quantify this effect but there are individual behaviors that clearly increase this; eg skitter ahead, move up and lock into new position in school

7. Other evidence that predation is impt:

genetic differences in schooling behav among populations exposed to preds and not.

8. Last comment:

there are predators that specialize on shoals or schools. Some preds ahead in arms race; herons will provide cover for shoals to take 'shelter' in.

3. Foraging and schools
1. benefits
1. faster location of food:

patchy food, higher density of foragers increases rate at which patches are found, then nonfinders join in feeding on that patch (fig. 12.10, p 320)

2. more time for feeding

bkz of less time needed for pred vigilance fig 12.11

3. overwhelming territories

schools of surgeonfish can graze their way through damselfish territories

2. cost:
1. increased competition for food already found
4. Migration
1. more accurate homing of salmon: averaging of individual errors
2. transfer of information: culture (Helfman and Schultz)

1. definition

mass movement from one habitat to another with characteristic regularity in time or according to life history stage; active or passive; feeding, breeding or wintering

2. types of migration:
1. diadromy
1. anadromy: to fresh to breed
2. catadromy: to salt to breed
3. amphidromy: migration not for purpose of breeding; both fresh and salt
2. oceanodromy: migration wholly within salt
3. potamodromy: migration wholly within fresh

1. Primarily in primitive bony fishes:

lampreys, sturgeons, eels, salmonids, and clupeids.

2. Otherwise rare and intermittent:

11 perciform families have species that are diadromous, but never the whole family

1. Within species
1. landlocking
1. many anadromous fishes
2. also in fw spawning amphidromous
3. replacement of marine feeding by fw feeding stage
4. different levels of anadromy within salmonids: fig 10.1, p 173 McDowall
5. loss of habit because of
1. natural geographical changes (e.g., tectonic)
2. strategic loss
3. human interference.
6. Loss of anadromous habit rapidly followed introduction of salmonids in many places e.g. Atlantic and pacific salmons to New Zealand
7. consequences: dwarfing; some life history changes
2. geographic variability within species
1. more anadromy at higher latitudes: brook trout in E U.S., brown trout in Europe; browns introduced to NZ. Also rainbows (fig. 7.3, p 113 McDowall)
2. Among species

Proportionally higher anadromy in high latitudes, catadromy in tropics (p. 117, fig. 7.6 McDowall)

In terms of absolute number of species, through warm temperate through subpolar regions, small but relatively constant # of anadromous spp (fig. 7.11)

1. Olfactory cues
1. plenty of evidence that juvenile anadromous fish imprint on substances in water and use this information later in life
2. Other navigation
1. olfactory cues probably not sufficient to find a home stream from the ocean.
2. Sun compass: most likely. Not much realistic evidence