10
M.L. Domeier
1.5 Spawning Aggregations in Non-reef Habitats
The growing base of literature relevant to spawning aggregations is dominated by
coral reef fi sh examples. However, fi shes in other habitats and latitudes certainly form
spawning aggregations but often lack the precision of timing and location found in
coral reef fi shes, and are therefore harder to describe. As a theoretical example of typical precision, an aggregation of a particular species may spawn over a 5-day period on
the edge of the same reef passage, at dusk on the full moon of July each and every
year. In another example, fi sh would aggregate to spawn over a particular feature of
the reef at the same time (or tidal cycle) each day over a protracted spawning season.
Chronobiological rhythms are important cues to the timing of spawning aggregations. Infradium rhythms dictate the spawning season, while circadian rhythms
dictate the fi ne scale, daily timing of spawning. Physical cycles of temperature,
salinity and tides may interact with chronobiological rhythms to dictate the timing
of spawning. Tropical marine habitats are relatively stable with respect to physical
cycles when compared to higher latitudes, allowing the timing of spawning aggregations to be controlled more by chronobiological cycles, thereby making them more
predictable. Higher latitude spawning aggregations are susceptible to unpredictable
variations in oceanographic factors, thereby making the timing of spawning aggregations less predictable than those that occur in tropical habitats. For example, temperature is an important controlling factor for the spawning of herring (Haegele and
Schweigert 1985 ) and inter-annual variation in water temperature can infl uence the
precise timing of spawning.
Year to year temporal variation in spawning aggregations is understandable when
physical cues are taken into consideration, but the spatial precision of spawning
aggregations can vary in both tropical and higher latitude habitats and this is harder
to understand. Some tropical spawning aggregations and temperate anadromous
spawning aggregations can be very precisely predictable with respect to location.
However, there are also examples of species from several different habitats that
aggregate in a general area each year, but the exact site of spawning is not always
the same. Pelagic fi shes and migratory coastal species appear to be more likely to
exhibit less spatial precision than demersal species. Croakers, herrings/sardines
(Clupeidae), mullets and fl ying fi shes (Exocoetidae) (see Appendix; Chap. 8 ; Bane
1965 ; Parin and Lakshminaraina 1993 ; Stevens et al. 2003 ; Casazza et al. 2005 ) are
examples of fi shes that form predictable spawning aggregations on a larger spatial
scale. Despite the lesser degree of spatial precision, these aggregations are still predicted, located and targeted by fi sheries, making them very relevant to this discussion in both biological and fi shery terms.
The overwhelming majority of documented spawning aggregations occur in
coastal habitats; however, examples from offshore and deep-sea habitats are emerging. Spawning aggregations of the commercially important orange roughy
( Hoplostethus atlanticus ) are well documented to seasonally occur over specifi c
seamounts between 700–1,000 m (Pankhurst 1988 ; Bell et al. 1992 ; Francis and
Clark 1998 ) . More recently described deep-sea spawning aggregation examples
include a sculpin, (Cottidae) Psychrolutes phrictus , and a cephalopod ( Graneledone sp .)
M.L. Domeier
1.5 Spawning Aggregations in Non-reef Habitats
The growing base of literature relevant to spawning aggregations is dominated by
coral reef fi sh examples. However, fi shes in other habitats and latitudes certainly form
spawning aggregations but often lack the precision of timing and location found in
coral reef fi shes, and are therefore harder to describe. As a theoretical example of typical precision, an aggregation of a particular species may spawn over a 5-day period on
the edge of the same reef passage, at dusk on the full moon of July each and every
year. In another example, fi sh would aggregate to spawn over a particular feature of
the reef at the same time (or tidal cycle) each day over a protracted spawning season.
Chronobiological rhythms are important cues to the timing of spawning aggregations. Infradium rhythms dictate the spawning season, while circadian rhythms
dictate the fi ne scale, daily timing of spawning. Physical cycles of temperature,
salinity and tides may interact with chronobiological rhythms to dictate the timing
of spawning. Tropical marine habitats are relatively stable with respect to physical
cycles when compared to higher latitudes, allowing the timing of spawning aggregations to be controlled more by chronobiological cycles, thereby making them more
predictable. Higher latitude spawning aggregations are susceptible to unpredictable
variations in oceanographic factors, thereby making the timing of spawning aggregations less predictable than those that occur in tropical habitats. For example, temperature is an important controlling factor for the spawning of herring (Haegele and
Schweigert 1985 ) and inter-annual variation in water temperature can infl uence the
precise timing of spawning.
Year to year temporal variation in spawning aggregations is understandable when
physical cues are taken into consideration, but the spatial precision of spawning
aggregations can vary in both tropical and higher latitude habitats and this is harder
to understand. Some tropical spawning aggregations and temperate anadromous
spawning aggregations can be very precisely predictable with respect to location.
However, there are also examples of species from several different habitats that
aggregate in a general area each year, but the exact site of spawning is not always
the same. Pelagic fi shes and migratory coastal species appear to be more likely to
exhibit less spatial precision than demersal species. Croakers, herrings/sardines
(Clupeidae), mullets and fl ying fi shes (Exocoetidae) (see Appendix; Chap. 8 ; Bane
1965 ; Parin and Lakshminaraina 1993 ; Stevens et al. 2003 ; Casazza et al. 2005 ) are
examples of fi shes that form predictable spawning aggregations on a larger spatial
scale. Despite the lesser degree of spatial precision, these aggregations are still predicted, located and targeted by fi sheries, making them very relevant to this discussion in both biological and fi shery terms.
The overwhelming majority of documented spawning aggregations occur in
coastal habitats; however, examples from offshore and deep-sea habitats are emerging. Spawning aggregations of the commercially important orange roughy
( Hoplostethus atlanticus ) are well documented to seasonally occur over specifi c
seamounts between 700–1,000 m (Pankhurst 1988 ; Bell et al. 1992 ; Francis and
Clark 1998 ) . More recently described deep-sea spawning aggregation examples
include a sculpin, (Cottidae) Psychrolutes phrictus , and a cephalopod ( Graneledone sp .)