Migratory environmental history of the grey mullet Mugil cephalus as revealed by otolith Sr:Ca ratios

Abstract

We used an electron probe microanalyzer (EPMA) to determine the migratory environmental history of the catadromous grey mullet Mugil cephalus from the Sr:Ca ratios in otoliths of 10 newly recruited juveniles collected from estuaries and 30 adults collected from estuaries, nearshore (coastal waters and bay) and offshore, in the adjacent waters off Taiwan. Mean (± SD) Sr:Ca ratios at the edges of adult otoliths increased significantly from 6.5 ± 0.9 × 10 -3 in estuaries and nearshore waters to 8.9 ± 1.4 × 10 -3 in offshore waters (p < 0.01), corresponding to increasing ambient salinity from estuaries and nearshore to offshore waters. The mean Sr:Ca ratios decreased significantly from the core (11.2 ± 1.2 × 10 -3 ) to the otolith edge (6.2 ± 1.4 × 10 -3 ) in juvenile otoliths (p < 0.001). The mullet generally spawned offshore and recruited to the estuary at the juvenile stage; therefore, these data support the use of Sr:Ca ratios in otoliths to reconstruct the past salinity history of the mullet. A life-history scan of the otolith Sr:Ca ratios indicated that the migratory environmental history of the mullet beyond the juvenile stage consists of 2 types. In Type 1 mullet, Sr:Ca ratios range between 4.0 × 10 -3 and 13.9 × 10 -3, indicating that they migrated between estuary and offshore waters but rarely entered the freshwater habitat. In Type 2 mullet, the Sr:Ca ratios decreased to a minimum value of 0.4 × 10 -3 , indicating that the mullet migrated to a freshwater habitat. Most mullet beyond the juvenile stage migrated from estuary to offshore waters, but a few mullet less than 2 yr old may have migrated into a freshwater habitat. Most mullet collected nearshore and offshore were of Type 1, while those collected from the estuaries were a mixture of Types 1 and 2. The mullet spawning stock consisted mainly of Type 1 fish. The growth rates of the mullet were similar for Types 1 and 2. The migratory patterns of the mullet were more divergent than indicated by previous reports of their catadromous behavior.

Habitat selection by grey mullets (Osteichthyes: Mugilidae) in Mediterranean estuaries: the role of salinity

“…M. cephalus and L. ramado are good osmoregulators, as they maintain a stable internal osmolality in a wide range of external salinity levels, including fresh water (Lasserre and Gallis, 1975;Nordlie and Lefler, 1975;Nordlie et al,, 1982;Thomas, 1984;Kulikova et al,, 1989 these two species, the cost of osmotic regulation is the lowest within the oligomesohaline range (Nordlie and Lefler, 1975;Cardona, 1994Cardona, , 2000 and therefore growth is expected to be highest within that range, although experimental evidence is available only for M. cephalus (Cardona, 2000). Thus, it is not surprising to find that these two species showed a strong preference for sites with a salinity level under 15, although adults may prefer more saline areas (Cardona, 2000;Chang et al, 2004). However, Chang et al, (2004) have revealed the existence of individual differences in the habitat preference of M. cephalus in Taiwan, as most specimens avoid freshwater sites throughout their life whereas others spend long periods there.…”

“…Thus, it is not surprising to find that these two species showed a strong preference for sites with a salinity level under 15, although adults may prefer more saline areas (Cardona, 2000;Chang et al, 2004). However, Chang et al, (2004) have revealed the existence of individual differences in the habitat preference of M. cephalus in Taiwan, as most specimens avoid freshwater sites throughout their life whereas others spend long periods there. Such variability may also be true for L. ramado, which is a species found over a wide range of salinity levels (Lafaille et al, 2002;Almeida, 2003).…”

Otolith chemistry to determine movements of diadromous and freshwater fish

“…For example, Chang et al (2004) found that habitat use changed with the age of mullet (Mugil cephalus), such that 26.7% and 10.5% of age 1 + and 2 + mullet respectively inhabited fresh water and that no fish 3 + or older inhabited fresh water. In contrast, the number of mullet that migrated offshore from freshwater and estuarine areas increased with age (Chang et al 2004).…”

Diadromous life cycle and behavioural plasticity in freshwater and estuarine Kuhliidae species (Teleostei) revealed by otolith microchemistry

“…Stable Sr:Ca ratios lower than 3.5 mg g −1 are generally associated with freshwater habitats (Chang et al 2004, Tabouret et al 2010, Feutry et al 2011). This species is thought to be catadromous and to reproduce at sea or in estuary plumes (Hogan & Nicholson 1987, Lewis & Hogan 1987).…”