MAJOR: ASPECTS OF ECOLOGY OF STRIPED MULLET 



Figure 3. — Experimental temperature (dashed line) and depth 

 (solid line) distributions for indicated mullet size ranges in the 

 80-cm deep tank at the indicated salinity (34, 15, or 0%o). No 

 experiments were conducted with fish 30-50 mm SL at 15%o 

 salinity. Each of the eight salinity-fish size range "conditions" 

 are subdivided into three observation intervals: 1) observation 

 interval 1, corresponding to the first three experimental obser- 

 vations (1-3); 2) observation interval 3 (7th-9th observations); 

 and 3) interval 5 (13th- 15th observations). Also presented are 

 mean depth (XD) and temperature ( XT) data. Sample size (n) is 

 based on the pooled data for the number of times each fish was 

 observed within the observation interval for all experiments at a 

 given salinity and for a given fish size range. Experiments varied 

 in duration and number of observations made. Thus, the sample 

 size fluctuates. See Table 1 for the actual (maximum) number of 

 fish and experiments for each salinity-fish size range condition. 



Field 



Mullet Distribution 



The initial appearance of the 17- to 35-mm SL 

 mullet prejuveniles, a distinct silvery, counter- 

 shaded pelagic stage (Hubbs 1958), in the es- 

 tuarine intertidal regions varied between 1972 

 and 1973. In 1972 they were observed and col- 

 lected along the tide line (the most shoreward edge 

 of falling or rising water, which is contiguous with 

 deeper offshore water) in sand and mud flat tide 

 pools and around freshwater streams and springs 

 at the end of January. In 1973 they did not appear 

 in these areas until the end of February. Pre- 

 juveniles were particularly abundant in areas 

 with the finest silt, mud, and/or sand particles 

 near the outlets of freshwater rivers, streams, 

 or springs. 



Fish 3=50 mm SL could be seen year around in 

 the intertidal areas. The main body of this study 

 concentrated on those fish that entered the inter- 

 tidal in 1972. Also observed were juveniles of the 

 1971 year class, fish ^80 mm SL, in the intertidal 

 in early 1972, and prejuveniles and juveniles of 

 the 1973 year class, «50 mm SL, in early 1973. 

 The disappearance of prejuveniles-juveniles from 

 the low tide intertidal swash zone (Hedgpeth 

 1957) and tide line regions appeared to be com- 

 pleted by the end of June each year, although 

 occasional schools were seen as late as August. 

 However, these schools were composed offish usu- 

 ally about 40 mm SL or larger, that moved with 

 the tide line. 



Prejuvenile mullet undergo metamorphosis to 

 juveniles after entering the estuarine intertidal 

 region. The most evident change is the loss of the 

 pelagic silvery coloration with a general darken- 



ing of all surfaces, especially the dorsal side. How- 

 ever, a general countershaded pattern remains. 

 Other less obvious changes include: the elongation 

 and convolution of the intestine, development of 

 adipose eyelids, transformation of the third anal 

 element from a soft ray to a spine, and changes in 

 the morphology of lips and teeth. Metamorphosis 

 is thought to be completed at about 50 mm SL 

 (Jacot 1920). 



During metamorphosis, diet and feeding habits 

 change. I found copepods in the stomach contents 

 of some prejuveniles in Hawaii in the estuarine 

 intertidal regions. Other prejuveniles and 

 juveniles had plant and animal material as well as 

 mud or silt in their stomachs. I found that sedi- 

 ments constituted the bulk of the diet of juvenile 

 mullet in some localities in Hawaii. In the es- 

 tuarine intertidal region around the island of 

 Oahu, the sizes of these injested particles ranged 

 from 0.02 to 0.60 mm in diameter. Odum (1968) 

 showed that fine particulate materials are a 

 source of adsorbed organic matter and microor- 

 ganisms, and are important in the diet of Mugil 

 cephalus along parts of the east coast of the United 

 States. The change in diet from copepods to plant 

 material and mud or silt presumably occurs con- 

 currently with changes in intestinal length, lips, 

 and teeth. After metamorphosis is completed, the 

 juvenile fish move into somewhat deeper interti- 

 dal water. 



Prejuveniles and juveniles of all sizes formed 

 schools ranging in size from tens to hundreds of 

 individuals. Prejuveniles and juveniles <50 mm 

 SL were always observed in the shallowest, warm- 

 est water near shore wherever they occurred (Ta- 

 ble 2). At low tide they were located along the tide 

 line, the shallowest water along estuarine 

 streams, and trapped in shallow mud flat and oc- 

 casionally sand tide pools (the swash zone). In- 

 tense continuous feeding activity was usually ob- 

 served. The substrate in the areas in which the 

 small mullet occurred was covered usually by the 

 finest inorganic sediment (sand and silt 0.02-0.60 

 mm in diameter). 



Salinity and temperature values changed daily 

 depending on tide level (water depth), wind, bot- 

 tom type (particle size, color, etc.), insolation, and 

 the location of springs and streams. Often a spatial 

 as well as temporal kaleidoscope of temperature 

 and salinity values was recorded, especially along 

 Wailupe Beach. 



On 15 March 1972 the last hour (1200-1300 h 

 local time) of a natural fish kill was observed in 



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