Spatial and ontogenetic variation in growth of nursery-bound juvenile lemon sharks, Negaprion brevirostris: a comparison of two age-assigning techniques

We compared growth rates of the lemon shark, Negaprion brevirostris, from Bimini, Bahamas and the Marquesas Keys (MK), Florida using data obtained in a multi-year annual census. We marked new neonate and juvenile sharks with unique electronic identity tags in Bimini and in the MK we tagged neonate and juvenile sharks. Sharks were tagged with tiny, subcutaneous transponders, a type of tagging thought to cause little, if any disruption to normal growth patterns when compared to conventional external tagging. Within the first 2 years of this project, no age data were recorded for sharks caught for the first time in Bimini. Therefore, we applied and tested two methods of age analysis: ( 1) a modified 'minimum convex polygon' method and ( 2) a new age-assigning method, the 'cut-off technique'. The cut-off technique proved to be the more suitable one, enabling us to identify the age of 134 of the 642 previously unknown aged sharks. This maximised the usable growth data included in our analysis. Annual absolute growth rates of juvenile, nursery-bound lemon sharks were almost constant for the two Bimini nurseries and can be best described by a simple linear model ( growth data was only available for age-0 sharks in the MK). Annual absolute growth for age-0 sharks was much greater in the MK than in either the North Sound (NS) and Shark Land (SL) at Bimini. Growth of SL sharks was significantly faster during the first 2 years of life than of the sharks in the NS population. However, in MK, only growth in the first year was considered to be reliably estimated due to low recapture rates. Analyses indicated no significant differences in growth rates between males and females for any area.

Warehouse, PNG Coffee Industry Board Office and Warehouse, Goroka

View of exterior wall to warehouse.

Downpipes, PNG Coffee Industry Board Office and Warehouse, Goroka

Detailed view of downpipes and drainage grill.

PNG Coffee Industry Board Office and Warehouse, Goroka

View past tiered amphitheatre and offices above to air strip beyond.

View along western elevation, PNG Coffee Industry Board Office and Warehouse, Goroka

View past timber blinds to balcony and timber sunscreens.

Under construction, PNG Coffee Industry Board Office and Warehouse, Goroka

View of post being hoisted into position during construction.

Warehouse, PNG Coffee Industry Board Office and Warehouse, Goroka

View of warehouse exterior.

Pole detail, PNG Coffee Industry Board Office and Warehouse, Goroka

Detailed view of poles used in construction. Poles were spliced in their length with steel bars (like 3 pin plugs) and these joints were restrained from splitting with steel strap belts. The belts were tightened with opposing wedges like the old Greene & Greene wrought iron detail.

Warehouse, PNG Coffee Industry Board Office and Warehouse, Goroka

View of warehouse exterior.

Roof structure, internal, PNG Coffee Industry Board Office and Warehouse, Goroka

View to underside of roof with steel beam and insulation.

Post and beam connection, PNG Coffee Industry Board Office and Warehouse, Goroka

Detailed view of cast iron brackets connecting beams and posts.

Front elevation, PNG Coffee Industry Board Office and Warehouse, Goroka

View of front elevation with entrance from exterior.

Post and beam connection, PNG Coffee Industry Board Office and Warehouse, Goroka

Detailed view of cast iron brackets connecting beams and posts.