300 



Fishery Bulletin 100(2) 



Long-term records of estuarine recruitment of early life- 

 history stages of eels are particularly relevant at this time, 

 when reduction in juveniles (but not elvers) to the upper 

 St. Lawrence River area in North America has been noted 

 (Castonguay et al., 1994a), and when catches of adults and 

 recruitment of elvers are declining in Europe (Castonguay 

 et al., 1994b). We therefore present subsamples of ages 

 along with our catch per effort (densities) for glass eels. 

 Earlier studies of eel otoliths used SEM to determine ag- 

 es, but we used light microscopy for comparison with such 

 studies. Castonguay (1986) aged A. rosti-ata leptocephali 

 captured in the Gulf of Maine, and his largest individual 

 of 49 mm TL (which would shrink during metamorphosis) 

 was 130 d. However, only the daily growth increments in 

 the elver gi'owth zone (area after the "transition" or "el- 

 ver" check) have been validated (Martin, 1995). He vali- 

 dated daily increments in the field over a one-month pe- 

 riod. Lecomte-Finiger (1992) aged otoliths of A. anguilla 

 elvers from several European locations, as did Antunes 

 and Tesch (1997). The latter suggested that daily incre- 

 ments oi A. anguilla may be underestimated because of 

 the "diffuse" (their term) nature of the metamorphosis 

 zone. More recently, Cieri and McCleave (2000) suggested 

 that there are a number of inconsistencies when growth 

 zones of leptocephali are compared with the same zone 

 in the otoliths of glass eels and juvenile American eels. 

 Both radii and ages were less in the older fish stages than 

 in the leptocephali. The possibility of resorption of otolith 

 material during metamorphosis (and subsequent oblitera- 

 tion of increments) led them to discourage the use of lar- 

 val eel otoliths for aging or back-calculating life history 

 events until these discrepancies could be explained. Al- 

 though the present authors could not validate increments 

 in the leptocephalus stage or metamorphosis stage (these 

 stages metamorphose before reaching North Carolina), we 

 collected samples to temporally validate daily increments 

 in the glass-eel stage. We tested the hypotheses that 1 ) the 

 increment number for glass eels at an upi'iver (freshwa- 

 ter) location would be greater than that for glass eels at 

 a lower (estuarine) sampling site by a difference (in days) 

 equal to the distance divided by the sum of the swimming 

 speed and tidal transport, and that 2) increment widths 

 for corresponding glass-eel portions of the otolith for fish 

 from the Bay of Fundy (New Brunswick sample) would 

 be narrower than for fish of warmer water (i.e. North Car- 

 olina! because the warmer waters would produce faster 

 growth which, in turn, could produce wider otolith incre- 

 ments. A New Jersey sample was also aged to represent an 

 intermediate geogi-aphic position between North Carolma 

 and New Brunswick. 



The objectives of this study were li to describe the 

 1985-95 annual recruitment of glass eels to the estuary 

 near Beaufort; 2) to present the variations in seasonal 

 densities of glass eels: 3) to analyze the seasonal length 

 frequency by weekly intei-vals, and 4) to compare mean 

 ages of glass eels at three locations along the eastern coast 

 of North America (North Carolina, New Jersey, and New 

 Brunswick). We also tested two hypotheses relevant to val- 

 idating daily deposition of otolith growth increments in 

 the glass-eel stage of Anguilla rostrata. 



Methods 



Collections 



Glass eels were collected from two sites in North Caro- 

 lina: 1 ) in the lower Newport River at Fivers Island, about 

 2 km inside Beaufort Inlet: and 2) at Black Creek, a small 

 tributary of the Newport River, at the entrance to a mill- 

 pond, about 9.5 km upriver from Beaufort. North Caro- 

 lina. The samples at Fivers Island were collected over the 

 10-year period 1985-95 with a 1x2 m neuston net fitted 

 with 945-um mesh and flow meter and suspended from 

 a bridge, except during 1985-86. when 60-cm bongo nets 

 were used. Details of the sampling protocol are given in 

 Warlen (1994). Samples were always collected at night 

 during midflood tide, from November to April. Density of 

 fish in the catches was standardized as the mean number 

 per 100 nr'. Additional samples were collected by dip net 

 from Black Creek just below a small dam leading into 

 a millpond (22 February and 20 March 1994). Samples 

 were also obtained from two areas north of North Caro- 

 lina: 1 ) Little Egg Inlet, New Jersey, at the site of the 

 Marine Field Station, State University of New Jersey, 

 Rutgers.Tuckerton, NJ (39°30'N. 74°14'W) on 21 Febru- 

 rary and 9 March 1994 (with a 1-m plankton net): 2) 

 elvers were captured from the Lepreau River, at the vil- 

 lage of Lepreau, New Brunswick, Canada, on the Bay of 

 Fundy (45°00'N, 66°20'W) on 6 June 1994. This sample 

 was collected with a 1-mm mesh dip net and was pre- 

 served in 70% ethanol. All other samples were preserved 

 in 950r ethanol, and then preserved in fresh 70% ethanol 

 after 24 h. 



Aging methods 



All eels were measured (TL to the nearest 0.1 mm) with 

 a Vernier caliper and saggital otoliths were removed, 

 washed, dried, and mounted on glass slides with thermal 

 cement, sulcus groove down. The otoliths were ground 

 with a series of wet grit papers (no. 600 to 1200i until 

 the core was visible, then polished with diamond paste, 

 after which they were aged by using an oil-immersion 

 lens from 1200 to 3100x. A subsample of 10 otoliths was 

 also sectioned (transverse) and pi-epared for reading, and 

 ages were compared with ages from whole otoliths from 

 the same fish. Sectioned otoliths had about 4% more rings 

 in the outer edge. Otolith increments were read from the 

 hatching ring outwards, as suggested by Lecomte-Finiger 

 ( 1992 ) and Tzeng ( 1996 ). Umezawa and Tsukamoto ( 1991 ) 

 found that no rings were formed during the incubation 

 period (5 days) of A. japonica. To maintain consistency 

 with other authors, we therefore added five days to our 

 ages. An optical imaging system was used to count incre- 

 ments and to measure increment widths and the distance 

 from the core to the first-feeding (exogenous) ring, etc. 

 The lowest increment width (distance between adjacent 

 dark rings) recorded was 0.326 p, a distance which was 

 probably close to the resolution minimum of our micro- 

 scope. Incremental counts were made of the leptocephalus 

 growth zone, the metamorphic zone, the glass-eel growth 



