Thomson. — Portobello Marine Fish-hatchery. 537 



Otago, which appears to be still in progress, there is still a great 

 extent of surface in the upper harbour over which the ebb and 

 flow of the tide act. An immense body of water is thus continu- 

 ally passing to and fro through the three channels which separate 

 the two main basins, and the scour keeps these channels relatively 

 deep. The conformation of the land also causes the prevalent 

 winds to blow with considerable force through these gaps in the 

 dividing barrier, and when a strong south-west wind is blowing 

 it drives through with immense force. 



The position of the hatchery is just at the most easterly of 

 these channels. The site covers 2| acres, but the coast-line is of 

 considerable length, owing to its deep indentations. The bays 

 on the north-west and north sides are extremely well sheltered 

 from the prevailing south-west winds by the high ground out of 

 which they are hollowed, and two of these bays have been 

 enclosed as retaining-ponds, and for the main hatchery buildings. 



The depth of water immediately outside the main embank- 

 ment at low water is about 18 in., and at high water from 6 ft. 6 in. 

 at ordinary to 8 ft. 6 in. at high spring tides. The bottom is soft 

 mud and sand, and deepens very slowly for a distance of about 

 500 ft., where from 12 ft. to 20 ft. is obtained in the channel 

 between the hatchery and the sandbank, which extends prac- 

 tically to the Maori JcaiJc, a distance of about four miles. This 

 bank causes the flood tide for about the first two hours to flow 

 from the main channel at Quarantine Island in a north-easterly 

 direction towards Otago Heads. To the west of the hatchery 

 the water in the channel is much deeper, and a great body of 

 water is continually passing up and down at every tide, with a 

 flow like a wide river. 



Operations were commenced in July, 1903, for the con- 

 struction of the hatchery, by enclosing a large bay on the 

 northern side of the site, having a width of about 100 ft. and a 

 length of 80 ft. An embankment, 14 ft. in width on the top, 

 and pitched on the outside with large rough stones, was thrown 

 across the entrance ; and a similar embankment or platform, 

 30 ft. in width, was formed within this enclosure, just under 

 the high ground to the west, for the erection of the hatchery 

 buildings, engine-house, &c. A concrete wall, 10 ft. high, 

 2 ft. 6 in. at the base and 1 ft. thick at the top, was then built 

 on the inside of the embankment, and a similar wall built across 

 the middle, dividing the enclosure into two ponds of the following 

 dimensions : length, 65 ft. ; width, 30 ft. ; depth, 4 ft. 6 in. to 

 7 ft. ; and capacity, 60,000 gallons. These are controlled by 

 means of screw-valves fitted into 9 in. earthenware pipes con- 

 necting with the outside water. The embankment has since 

 been planted with suitable native shrubs and sown in grass. 



